v1.2 mobile PWA: installable app + mobile-first UI

- Installable PWA: manifest.json (standalone, portrait, maskable icons),
  theme-color + apple-mobile-web-app meta, generated 192/512 PNG icons,
  service worker (network-first, never caches /api/).
- Mobile UI (≤720px): sticky blurred header, agent grid -> horizontal
  snap-scroll carousel, fixed bottom composer with safe-area insets,
  modals -> full-screen bottom sheets, 16px inputs (no iOS zoom), bigger
  touch targets, icon-only header actions.
- /app remains the app shell; / is the landing page.

static/manifest.json

@@ -0,0 +1,14 @@
+{
+  "name": "Astraea — Washington Family Law Assistant",
+  "short_name": "Astraea",
+  "description": "Eight specialist AI attorneys grounded in Washington statute and case law. Not legal advice.",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#070b1a",
+  "theme_color": "#070b1a",
+  "orientation": "portrait-primary",
+  "icons": [
+    { "src": "/static/icon-192.png", "sizes": "192x192", "type": "image/png", "purpose": "any maskable" },
+    { "src": "/static/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "any maskable" }
+  ]
+}