Reduce egress costs, add PWA support, fix Polymarket and Railway relay

Egress optimization:
- Add s-maxage + stale-while-revalidate to all API endpoints for Vercel CDN caching
- Add vercel.json with immutable caching for hashed assets
- Add gzip compression to sidecar responses >1KB
- Add gzip to Railway RSS responses (4 paths previously uncompressed)
- Increase polling intervals: markets/crypto 60s→120s, ETF/macro/stablecoins 60s→180s
- Remove hardcoded Railway URL from theater-posture.js (now env-var only)

PWA / Service Worker:
- Add vite-plugin-pwa with autoUpdate strategy
- Cache map tiles (CacheFirst), fonts (StaleWhileRevalidate), static assets
- NetworkOnly for all /api/* routes (real-time data must be fresh)
- Manual SW registration (web only, skip Tauri)
- Add offline fallback page
- Replace manual manifest with plugin-generated manifest

Polymarket fix:
- Route dev proxy through production Vercel (bypasses JA3 blocking)
- Add 4th fallback tier: production URL as absolute fallback

Desktop/Sidecar:
- Dual-backend cache (_upstash-cache.js): Redis cloud + in-memory+file desktop
- Settings window OK/Cancel redesign
- Runtime config and secret injection improvements

api/rss-proxy.js

@@ -223,7 +223,7 @@ export default async function handler(req) {
       status: response.status,
       headers: {
         'Content-Type': 'application/xml',
-        'Cache-Control': 'public, max-age=300',
+        'Cache-Control': 'public, max-age=300, s-maxage=300, stale-while-revalidate=60',
         ...corsHeaders,
       },
     });