feat: proper logo, favicon, and pwa icons

- replace placeholder house svg with clean geometric house mark
  on indigo-700 (#4338CA) — roof triangle, body, door cutout
- add favicon.svg with prefers-color-scheme dark variant
- add icon-16/32 sizes; regenerate all pngs from svg via sharp
- update BrandMark component to use inline svg house instead of 'f'
- wire favicon + sized pngs into layout metadata
- fix middleware to allow icon/manifest/favicon paths without auth
  (android launcher fetches icons in a cookieless system context)
- fix getCurrentSession() to redirect to /login instead of throwing
  when session cookie is stale/invalid

public/manifest.webmanifest

@@ -4,23 +4,26 @@
   "description": "Family coordination app",
   "start_url": "/",
   "display": "standalone",
-  "background_color": "#ffffff",
-  "theme_color": "#4F46E5",
+  "background_color": "#4338CA",
+  "theme_color": "#4338CA",
   "icons": [
     {
       "src": "/icon-192.png",
       "sizes": "192x192",
-      "type": "image/png"
+      "type": "image/png",
+      "purpose": "any"
     },
     {
       "src": "/icon-384.png",
       "sizes": "384x384",
-      "type": "image/png"
+      "type": "image/png",
+      "purpose": "any"
     },
     {
       "src": "/icon-512.png",
       "sizes": "512x512",
-      "type": "image/png"
+      "type": "image/png",
+      "purpose": "any"
     },
     {
       "src": "/icon-512-maskable.png",