perf(rss): route RSS direct to Railway, skip Vercel middleman (#961)

* perf(rss): route RSS direct to Railway, skip Vercel middleman

Vercel /api/rss-proxy has 65% error rate (207K failed invocations/12h).
Route browser RSS requests directly to Railway (proxy.worldmonitor.app)
via Cloudflare CDN, eliminating Vercel as middleman.

- Add VITE_RSS_DIRECT_TO_RELAY feature flag (default off) for staged rollout
- Centralize RSS proxy URL in rssProxyUrl() with desktop/dev/prod routing
- Make Railway /rss public (skip auth, keep rate limiting with CF-Connecting-IP)
- Add wildcard *.worldmonitor.app CORS + always emit Vary: Origin on /rss
- Extract ~290 RSS domains to shared/rss-allowed-domains.cjs (single source of truth)
- Convert Railway domain check to Set for O(1) lookups
- Remove rss-proxy from KEYED_CLOUD_API_PATTERN (no longer needs API key header)
- Add edge function test for shared domain list import

* fix(edge): replace node:module with JSON import for edge-compatible RSS domains

api/_rss-allowed-domains.js used createRequire from node:module which is
unsupported in Vercel Edge Runtime, breaking all edge functions (including
api/gpsjam). Replaced with JSON import attribute syntax that works in both
esbuild (Vercel build) and Node.js 22+ (tests).

Also fixed middleware.ts TS18048 error where VARIANT_OG[variant] could be
undefined.

* test(edge): add guard against node: built-in imports in api/ files

Scans ALL api/*.js files (including _ helpers) for node: module imports
which are unsupported in Vercel Edge Runtime. This would have caught the
createRequire(node:module) bug before it reached Vercel.

* fix(edge): inline domain array and remove NextResponse reference

- Replace `import ... with { type: 'json' }` in _rss-allowed-domains.js
  with inline array — Vercel esbuild doesn't support import attributes
- Replace `NextResponse.next()` with bare `return` in middleware.ts —
  NextResponse was never imported

* ci(pre-push): add esbuild bundle check and edge function tests

The pre-push hook now catches Vercel build failures locally:
- esbuild bundles each api/*.js entrypoint (catches import attribute
  syntax, missing modules, and other bundler errors)
- runs edge function test suite (node: imports, module isolation)

.husky/pre-push

@@ -9,5 +9,18 @@ for f in scripts/*.cjs; do
   [ -f "$f" ] && node -c "$f" || exit 1
 done
 
+echo "Running edge function bundle check..."
+for f in api/*.js; do
+  case "$(basename "$f")" in _*) continue;; esac
+  npx esbuild "$f" --bundle --format=esm --platform=browser --outfile=/dev/null 2>/dev/null || {
+    echo "ERROR: esbuild failed to bundle $f — this will break Vercel deployment"
+    npx esbuild "$f" --bundle --format=esm --platform=browser --outfile=/dev/null
+    exit 1
+  }
+done
+
+echo "Running edge function tests..."
+node --test tests/edge-functions.test.mjs || exit 1
+
 echo "Running version sync check..."
 npm run version:check || exit 1