fix: prevent CF caching SPA HTML + Polymarket bandwidth optimization (#1058)

* perf: reduce Vercel data transfer costs with CDN optimization

- Increase polling intervals (markets 8→12min, feeds 15→20min, crypto 8→12min)
- Increase background tab hiddenMultiplier from 10→30 (polls 3x less when hidden)
- Double CDN s-maxage TTLs across all cache tiers in gateway
- Add CDN-Cache-Control header for Cloudflare-specific longer edge caching
- Add ETag generation + 304 Not Modified support in gateway (zero-byte revalidation)
- Add CDN-Cache-Control to bootstrap endpoint
- Add explicit SPA rewrite rule in vercel.json for CF proxy compatibility
- Add Cache-Control headers for /map-styles/, /data/, /textures/ static paths

* fix: prevent CF from caching SPA HTML + reduce Polymarket bandwidth 95%

- vercel.json: apply no-cache headers to ALL SPA routes (same regex as
  rewrite rule), not just / and /index.html — prevents CF proxy from
  caching stale HTML that references old content-hashed bundle filenames
- Polymarket: add server-side aggregation via Railway seed script that
  fetches all tags once and writes to Redis, eliminating 11-request
  fan-out per user per poll cycle
- Bootstrap: add predictions to hydration keys for zero-cost page load
- RPC handler: read Railway-seeded bootstrap key before falling back to
  live Gamma API fetch
- Client: 3-strategy waterfall (bootstrap → RPC → fan-out fallback)

vercel.json

@@ -25,13 +25,7 @@
       ]
     },
     {
-      "source": "/",
-      "headers": [
-        { "key": "Cache-Control", "value": "no-cache, no-store, must-revalidate" }
-      ]
-    },
-    {
-      "source": "/index.html",
+      "source": "/((?!api|assets|favico|map-styles|data|textures|sw\\.js|manifest\\.webmanifest|offline\\.html|robots\\.txt|sitemap\\.xml|llms\\.txt|llms-full\\.txt|\\.well-known).*)",
       "headers": [
         { "key": "Cache-Control", "value": "no-cache, no-store, must-revalidate" }
       ]