fix(ui): bottom padding + close-screen button removed + sidebar collapse + quiet loguru

Four issues batched together since they all touch the GUI shell:

- ``stMainBlockContainer``'s ``padding-bottom`` bumped from 0.75rem
  → 4rem (~one button-height of free space above the fixed Help/Close
  footer). The last line of content on a page that fills the viewport
  was previously sitting flush against the footer's top border.

- Farewell overlay's "Close this window" button removed per UX
  request. The auto-dismiss path is now the only flow: try
  programmatic close (works in Chrome/Edge ``--app`` windows);
  failing that, surface the hint and redirect the parent window to
  ``about:blank`` after a short timeout. Previously the user had to
  click the button to get the same fallback. The
  ``quit.close_window_button`` i18n key is retained as a no-op for
  now in case the button comes back; nothing references it.

- Sidebar collapse → expand was broken: clicking « collapsed the
  sidebar but the » expand-back affordance was invisible. Two causes
  pulled apart:

   1. ``.dt-brand { flex: 1 }`` was eating the entire
      ``stSidebarHeader`` width, squeezing Streamlit's
      ``stSidebarCollapseButton`` off the right edge. Changed to
      ``margin: 0 auto 0 0`` so the brand keeps its natural width
      and the chevron has room to live next to it.

   2. The "hide Streamlit chrome" toolbar block was listing
      ``stToolbar`` and ``stToolbarActions`` for ``display: none``
      — but the post-collapse re-open button
      (``stExpandSidebarButton``) lives inside ``stToolbar``, so
      hiding the container killed the button too. Dropped both
      container testids from the hide list and kept the per-icon
      rules for ``stMainMenu`` / ``stAppDeployButton`` /
      ``stStatusWidget`` / ``stDecoration``.

- Loguru's stderr sink quieted in GUI mode. ``src/gui/app.py`` now
  runs ``logger.remove()`` + ``logger.add(sys.stderr, level="ERROR",
  …)`` at the top so internal ``logger.debug`` / ``logger.warning``
  breadcrumbs (e.g.
  ``standardize_dataframe: 7/31 cells were unparseable``) no longer
  print to the terminal when the user runs ``python -m src.gui``.
  CLI entry points already do the same configuration per-script.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/gui/components/_legacy.py

@@ -43,17 +43,17 @@ header[data-testid="stHeader"] {
     background: transparent !important;
     height: 0 !important;
 }
-/* Hide every Streamlit-shipped icon button in the header band:
-   hamburger menu, deploy button, status / running indicator,
-   toolbar action stacks. ``toolbarMode = "viewer"`` already suppresses
-   most of these but newer Streamlit releases keep emitting them with
-   tiny inline styles, so we belt-and-suspenders the visibility from
-   CSS too. */
+/* Hide the noisy Streamlit-shipped icon buttons in the header band
+   (hamburger menu, deploy button, status / running indicator). We
+   deliberately do NOT hide ``stToolbar`` or ``stToolbarActions`` as
+   containers — those wrap ``stExpandSidebarButton`` which is the
+   ONLY path back to an expanded sidebar after the user collapses it.
+   ``toolbarMode = "viewer"`` already suppresses most of these icons;
+   the CSS belt-and-suspenders the visibility for newer Streamlit
+   releases that keep emitting them with inline styles. */
 #MainMenu,
 [data-testid="stMainMenu"],
 [data-testid="stAppDeployButton"],
-[data-testid="stToolbar"],
-[data-testid="stToolbarActions"],
 [data-testid="stStatusWidget"],
 [data-testid="stDecoration"] {
     display: none !important;
@@ -104,7 +104,11 @@ footer {
 .stMainBlockContainer,
 [data-testid="stMainBlockContainer"] {
     padding-top: 0.5rem !important;
-    padding-bottom: 0.75rem !important;
+    /* +4rem buys a comfortable read of the last line of content on a
+       page that fills the viewport: the fixed Help/Close footer is
+       ~36px (≈2.25rem) tall and we want at least a button-height of
+       free space between the last widget and the footer's top edge. */
+    padding-bottom: 4rem !important;
 }
 /* Scale content to fit app window */
 .stApp {
@@ -192,14 +196,32 @@ body, .stApp {
    text. Injected into ``[data-testid="stSidebarHeader"]`` by the JS
    below; ``stLogoSpacer`` is hidden so the brand block takes its
    place flush against the left edge of the sidebar header. */
+/* The brand sits next to Streamlit's sidebar collapse button inside
+   ``stSidebarHeader``. ``flex: 1`` would steal all the horizontal
+   space and squash the collapse chevron out of view — once collapsed
+   the user would have no way to reopen the sidebar. Keep the brand
+   at its natural width and let the header's flex layout leave room
+   for the chevron on the right. */
 .dt-brand {
     display: flex !important;
     align-items: center;
     gap: 10px;
     padding: 0 0 0 4px;
-    margin: 0;
-    height: 100%;
-    flex: 1;
+    margin: 0 auto 0 0;
+}
+/* Belt-and-suspenders: keep the in-sidebar collapse button + the
+   out-of-sidebar collapsed control reachable. The latter is what
+   appears on the page edge once the sidebar slides shut. */
+[data-testid="stSidebarCollapseButton"],
+[data-testid="stSidebarCollapseButton"] button {
+    display: inline-flex !important;
+    visibility: visible !important;
+    opacity: 1 !important;
+}
+[data-testid="stSidebarCollapsedControl"] {
+    display: flex !important;
+    visibility: visible !important;
+    z-index: 9999 !important;
 }
 /* "Letter D (sans)" wordmark per Business/DataTools/app_icons.html
    §03: 28px ink-filled rounded square, cream "D" in Geist 700 with
@@ -1274,12 +1296,7 @@ _FAREWELL_SCRIPT_TEMPLATE = """
         'border-radius:12px;background:#161922;max-width:480px;">' +
         '<h1 style="margin:0 0 8px 0;font-weight:600;letter-spacing:-0.01em;">' +
         '__TITLE__</h1>' +
-        '<p style="opacity:0.7;margin:0 0 20px 0;">__SUBTITLE__</p>' +
-        '<button id="datatools-close-btn" style="' +
-        'background:#6ee7b7;color:#052e1a;font-weight:600;' +
-        'padding:10px 20px;border-radius:8px;border:none;' +
-        'font-size:15px;cursor:pointer;font-family:inherit;">' +
-        '__CLOSE_BTN__</button>' +
+        '<p style="opacity:0.7;margin:0;">__SUBTITLE__</p>' +
         '<p id="datatools-close-hint" style="' +
         'display:none;font-size:13px;opacity:0.6;margin:14px 0 0 0;">' +
         '__CLOSE_HINT__</p>' +
@@ -1310,21 +1327,21 @@ _FAREWELL_SCRIPT_TEMPLATE = """
       // push to history.
       try { win.location.replace('about:blank'); } catch (e) {}
     }
-    function wireClose(doc, win) {
-      var btn = doc.getElementById('datatools-close-btn');
-      if (!btn) return;
-      btn.onclick = function () {
-        var standalone = isStandalone(win);
-        if (tryClose(win)) return;
-        // Close failed (or definitely will fail in a regular tab).
-        // Surface the hint immediately, then redirect to about:blank
-        // after a short delay so the user has a moment to read why.
-        var hint = doc.getElementById('datatools-close-hint');
-        if (hint) hint.style.display = 'block';
-        setTimeout(function () {
-          if (!win.closed) fallbackToBlank(win);
-        }, standalone ? 250 : 1500);
-      };
+    function autoDismiss(doc, win) {
+      // Try the programmatic close first — succeeds in Chrome/Edge
+      // --app windows. If it fails (regular browser tab), surface the
+      // hint and auto-redirect to about:blank so the user lands on a
+      // clean page instead of the frozen farewell overlay. The "Close
+      // this window" button used to drive the same flow on click; we
+      // dropped that affordance per UX request, so this auto-timer is
+      // the only path on regular tabs.
+      var standalone = isStandalone(win);
+      if (tryClose(win)) return;
+      var hint = doc.getElementById('datatools-close-hint');
+      if (hint) hint.style.display = 'block';
+      setTimeout(function () {
+        if (!win.closed) fallbackToBlank(win);
+      }, standalone ? 400 : 2500);
     }
     try {
       var doc = window.top.document;
@@ -1332,17 +1349,12 @@ _FAREWELL_SCRIPT_TEMPLATE = """
       if (!doc.getElementById('datatools-farewell-overlay')) {
         doc.body.appendChild(buildOverlay(doc));
       }
-      wireClose(doc, win);
-      // Auto-close attempt on first paint — succeeds in Chrome --app
-      // windows, fails silently on regular tabs (and we don't redirect
-      // automatically here; the manual button drives that path so the
-      // user is in control).
-      tryClose(win);
+      autoDismiss(doc, win);
     } catch (e) {
       // Cross-origin access denied (shouldn't happen given Streamlit's
       // sandbox flags, but fall back gracefully): cover this iframe.
       document.body.appendChild(buildOverlay(document));
-      wireClose(document, window);
+      autoDismiss(document, window);
     }
   })();
 </script>