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/components/_legacy.py

@@ -414,6 +414,60 @@ div[data-testid="stContainer"][data-border="true"] {
     border: 1px solid var(--border) !important;
     overflow: hidden !important;
 }
+
+/* ---------- Stats overview ---------- */
+/* 4-card grid shown above the per-file findings on the home page,
+   summarizing the most recent analysis run. Numeric values use the
+   "Display number" row from geist_spec.md §4 — Geist 28px / 600 /
+   -0.03em — and the severity-tinted variants pick up ``--warn`` /
+   ``--info`` from theme.py. */
+.dt-stats {
+    display: grid;
+    grid-template-columns: repeat(4, 1fr);
+    gap: 12px;
+    margin: 8px 0 20px;
+}
+.dt-stat {
+    background: var(--surface);
+    border: 1px solid var(--border);
+    border-radius: var(--r-lg);
+    padding: 16px 18px;
+    box-shadow: 0 1px 2px rgba(28,25,23,0.03);
+}
+.dt-stat-label {
+    font-size: 11.5px;
+    text-transform: uppercase;
+    letter-spacing: 0.08em;
+    color: var(--ink-tertiary);
+    font-weight: 500;
+    margin-bottom: 6px;
+    line-height: 1.4;
+}
+.dt-stat-value {
+    font-family: var(--font-sans);
+    font-size: 28px;
+    font-weight: 600;
+    letter-spacing: -0.03em;
+    line-height: 1;
+    color: var(--ink);
+    display: flex;
+    align-items: baseline;
+    gap: 6px;
+}
+.dt-stat-unit {
+    font-family: var(--font-sans);
+    font-size: 12px;
+    font-weight: 400;
+    color: var(--ink-tertiary);
+    letter-spacing: 0;
+}
+.dt-stat.is-warn .dt-stat-value { color: var(--warn); }
+.dt-stat.is-info .dt-stat-value { color: var(--info); }
+.dt-stat.is-success .dt-stat-value { color: var(--success); }
+
+@media (max-width: 900px) {
+    .dt-stats { grid-template-columns: repeat(2, 1fr); }
+}
 </style>
 """