fix(footer,nav): left-justify buttons, drop per-page caption bar, hide sidebar Close

Three small follow-ups to the sticky-footer rework:

- Left-justify the footer buttons (and reposition the Help popover
  to anchor at the left edge so it lines up with its trigger).
- Remove the per-page ``st.divider() + st.caption("Runs locally…")``
  trailing block from all 9 tool pages. The new sticky footer
  covers that text, so it was rendering as an empty white bar at
  the bottom of each tool page.
- Hide the Close entry from the sidebar nav via CSS. The page stays
  registered with st.navigation so /close is still routable for the
  sticky-footer Close button — only the sidebar link + its section
  header are hidden (via :has() on stNavSection).

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

src/gui/components/_legacy.py

@@ -60,6 +60,24 @@ header[data-testid="stHeader"] {
 footer {
     display: none !important;
 }
+/* Hide the "Close" entry from the sidebar nav — the page is kept
+   registered so the sticky-footer Close link can still route to
+   /close, but the sidebar entry is redundant and risks mis-clicks. */
+[data-testid="stSidebarNav"] a[href$="/close"],
+[data-testid="stSidebarNav"] a[href$="/close/"] {
+    display: none !important;
+}
+/* Hide the entire "Close" section so its header label doesn't
+   orphan above the hidden link. Streamlit tags each nav section
+   with ``data-testid="stNavSection"``; the :has() selector picks
+   only the one containing the close link. Modern browsers (Chrome
+   105+, Safari 15.4+, Firefox 121+) all support it; older
+   browsers fall back to showing the empty header, which is
+   visually harmless. */
+[data-testid="stSidebarNav"] [data-testid="stNavSection"]:has(a[href$="/close"]),
+[data-testid="stSidebarNav"] [data-testid="stNavSection"]:has(a[href$="/close/"]) {
+    display: none !important;
+}
 /* Reclaim top padding lost from hidden header. Slim the bottom too —
    Streamlit's default leaves several rems below the last widget. */
 .stAppViewBlockContainer,
@@ -572,7 +590,7 @@ def render_sticky_footer() -> None:
     z-index: 2147483646 !important;
     display: flex !important;
     align-items: center !important;
-    justify-content: flex-end !important;
+    justify-content: flex-start !important;
     gap: 0.4rem !important;
     font-family: system-ui, -apple-system, sans-serif !important;
     box-sizing: border-box !important;
@@ -605,7 +623,7 @@ def render_sticky_footer() -> None:
 }
 #datatools-help-popover {
     position: fixed !important;
-    right: 0.75rem !important;
+    left: 0.75rem !important;
     bottom: 44px !important;
     background: white !important;
     border: 1px solid rgba(49, 51, 63, 0.25) !important;