style(design): migrate to DESIGN.md system

Full visual migration: Space Grotesk + DM Sans + JetBrains Mono fonts,
warm amber two-accent system (amber=state, blue=action), dark mode with
CSS vars + localStorage + FOUC prevention, mobile bottom nav (5 tabs),
full-width tables, error/skipped dot glow, ~13 hardcoded hex replaced
with CSS vars in 4 JS files, 5 new E2E tests.

Files: style.css (full rewrite), base.html (fonts, theme script, dark
toggle, bottom nav), settings.html (dark toggle card), dashboard.js,
logs.js, mappings.js, settings.js (color vars), 5 templates (bnav
active blocks), test_design_system_e2e.py (NEW).

Cache-bust: style.css?v=18, shared.js?v=14, dashboard.js?v=27,
logs.js?v=13, mappings.js?v=12, settings.js?v=8

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/static/js/dashboard.js

@@ -119,7 +119,7 @@ function updateSyncPanel(data) {
         }
         if (st) {
             st.textContent = lr.status === 'completed' ? '\u2713' : '\u2715';
-            st.style.color = lr.status === 'completed' ? '#10b981' : '#ef4444';
+            st.style.color = lr.status === 'completed' ? 'var(--success)' : 'var(--error)';
         }
     }
 }
@@ -342,7 +342,7 @@ async function loadDashOrders() {
                     const totalStr = o.order_total ? Number(o.order_total).toFixed(2) : '';
                     return `<div class="flat-row" onclick="openDashOrderDetail('${esc(o.order_number)}')" style="font-size:0.875rem">
                         ${statusDot(o.status)}
-                        <span style="color:#6b7280" class="text-nowrap">${dateFmt}</span>
+                        <span style="color:var(--text-muted)" class="text-nowrap">${dateFmt}</span>
                         <span class="grow truncate fw-bold">${esc(name)}</span>
                         <span class="text-nowrap">x${o.items_count || 0}${totalStr ? ' · <strong>' + totalStr + '</strong>' : ''}</span>
                     </div>`;