feat(ui): Material icons in sidebar + stats overview on home

Two pieces of the mockup 2 layout that hadn't landed yet:

1. Sidebar nav icons — emoji glyphs (🧹 ✂️ 🔍 …) swapped for
   Streamlit's ``:material/<name>:`` syntax, picking the outline
   Material Symbol that best matches each mockup SVG:

       Home               → :material/home:
       Fix Missing Values → :material/help_outline:
       Find Unusual Vals  → :material/insights:
       Clean Text         → :material/text_format:
       Standardize Fmts   → :material/format_list_bulleted:
       Find Duplicates    → :material/search:
       Quality Check      → :material/check_circle:
       Map Columns        → :material/view_column:
       Combine Files      → :material/account_tree:
       Auto Workflows     → :material/auto_awesome:
       Activate           → :material/key:
       Close              → :material/close:

   Streamlit injects the icon name as a literal ligature inside a
   first-child ``<span>`` of the nav anchor, expected to render
   through the Material Symbols font. theme.py's base rule was
   forcing Geist on every span under ``stSidebarNav``, turning the
   ligatures back into plain text labels — added a structural
   exception that targets ``[data-testid="stSidebarNavLink"] >
   span:first-child`` (and any descendant), restoring the Material
   font family, neutralizing the inherited ``ss01/cv01/cv11``
   feature settings, and sizing to 18px.

   Also stripped the leading emojis from every page title in the
   en/es i18n packs (``home.title``, ``close_page.title``,
   ``activation.title``, ``tools.*.page_title``) — the icons live
   in the sidebar now, the page H1 no longer needs to carry one.

2. Stats overview on home — new ``_render_stats_overview`` in
   _home.py emits a 4-card grid above the per-file findings panels:
   Files analyzed, Total findings, Warnings (severity ``warn`` ∪
   ``error``), Info (severity ``info``). Card layout follows the
   mockup §stats verbatim — Geist 28px / 600 / -0.03em for the
   numeric value (the "Display number" row in spec §4), tiny
   uppercase tracked label, paper-surface card with the standard
   warm border + faint shadow. The Warnings / Info cards tint the
   number with ``--warn`` / ``--info`` when the count is non-zero.

CSS for ``.dt-stats / .dt-stat / .dt-stat-label / .dt-stat-value /
.dt-stat-unit`` added to ``_DESIGN_TOKENS_CSS``; falls to a
2-column grid below 900px viewport, matching the mockup's media
query.

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

src/gui/_home.py

@@ -36,6 +36,61 @@ class _StashedUpload:
         return self._data
 
 
+def _render_stats_overview(findings_by_file: dict) -> None:
+    """4-card grid above the per-file findings — summarizes the run.
+
+    Card layout follows ``datatools_layout_redesign2.html`` §stats:
+    Files analyzed, Total findings, Warnings (severity ``warn`` ∪
+    ``error``), Info (severity ``info``). The warn + info cards are
+    tinted via ``.is-warn`` / ``.is-info`` modifiers that read the
+    severity colors theme.py declares.
+    """
+    import html as _html
+
+    n_files = len(findings_by_file)
+    all_findings = [f for fs in findings_by_file.values() for f in fs]
+    n_total = len(all_findings)
+    # Mockup groups errors with warnings on the "to review" card —
+    # both demand the user act. ``info`` is the lower-priority pile.
+    n_warn = sum(1 for f in all_findings if f.severity in ("warn", "error"))
+    n_info = sum(1 for f in all_findings if f.severity == "info")
+
+    def _card(label: str, value: int, unit: str = "", kind: str = "") -> str:
+        cls = "dt-stat" + (f" {kind}" if kind else "")
+        unit_html = (
+            f'<span class="dt-stat-unit">{_html.escape(unit)}</span>'
+            if unit else ""
+        )
+        return (
+            f'<div class="{cls}">'
+            f'<div class="dt-stat-label">{_html.escape(label)}</div>'
+            f'<div class="dt-stat-value">{value}{unit_html}</div>'
+            f"</div>"
+        )
+
+    cards = (
+        _card("Files analyzed", n_files)
+        + _card("Total findings", n_total)
+        + _card(
+            "Warnings",
+            n_warn,
+            unit="to review" if n_warn else "",
+            kind="is-warn" if n_warn else "",
+        )
+        + _card(
+            "Info",
+            n_info,
+            unit="suggestions" if n_info else "",
+            kind="is-info" if n_info else "",
+        )
+    )
+
+    st.markdown(
+        f'<div class="dt-stats">{cards}</div>',
+        unsafe_allow_html=True,
+    )
+
+
 def _sync_uploader_to_home_uploads() -> None:
     """``on_change`` callback for the home-page file_uploader.
 
@@ -272,6 +327,11 @@ def _home_page() -> None:
 
     if findings_by_file:
         st.divider()
+        # Overview row before drilling into per-file detail. Mockup
+        # layout (datatools_layout_redesign2.html §stats) puts a
+        # 4-card summary above the findings panels so the user can
+        # eyeball the run before expanding any one file.
+        _render_stats_overview(findings_by_file)
         # Preserve the upload-stash order so the user sees results in
         # the same order they appear in the file list above.
         for name in home_uploads: