feat(frontend): mobile bottom nav, chatbot overhaul, responsive polish

- MobileNav: safe-area-aware bottom tab bar (< md), mirrors desktop nav
- Chatbot: timestamps, per-message copy, retry-on-fail, auto-grow composer,
  MarkdownLite (XSS-safe React nodes, no dangerouslySetInnerHTML)
- AppFrame: NavRail (md+) + MobileNav (< md) + bottom content padding
- Design system: SignalTone ambient (signal/amber/vermilion) driving WebGL
  haze + topbar status pill; SectionHeader/MetricTile; globals.css tokens
- Views: dashboard hero + AmbientField, analysis/media responsive grids

services/frontend/src/app/(dashboard)/analysis/view.tsx

@@ -47,7 +47,9 @@ export function AnalysisView() {
           <Sparkles className="size-5 text-signal" />
           <div>
             <div className="eyebrow">Semantic search</div>
-            <h2 className="display text-2xl text-ink">Search the archive</h2>
+            <h2 className="display text-balance text-2xl text-ink">
+              Search the archive
+            </h2>
           </div>
         </div>
         <div className="relative mt-4">