fix: call OpenSky API directly from browser to bypass Vercel IP blocks (#1)

* fix: switch flights API to edge runtime, lower timeouts

- Switch to Edge Runtime (30s timeout on ALL Vercel plans, near-zero cold starts)
- Lower FETCH_TIMEOUT_MS from 20s to 8s (prevents Vercel killing the function)
- Lower TOKEN_TIMEOUT_MS from 5s to 3s
- Replace Buffer.from() with btoa() for edge compatibility
- Remove maxDuration (not needed for edge functions)

Fixes 502 Bad Gateway on Vercel deployments caused by Hobby plan's
10s function timeout being exceeded by the 20s fetch timeout.

* fix: revert edge runtime, keep reduced timeouts

Edge runtime caused 500 on Vercel. Reverted to Node.js serverless
with reduced timeouts only:
- FETCH_TIMEOUT_MS: 20s -> 8s
- TOKEN_TIMEOUT_MS: 5s -> 3s
- Restored Buffer.from() for basic auth

* fix: handle DOMException unavailability in Vercel runtime

- Fix TypeError: 'Right-hand side of instanceof is not an object'
  caused by DOMException not existing in Vercel's server runtime
- Use safe abort detection: check err.name === 'AbortError' on Error
  first, then conditionally check DOMException if available
- Restore TOKEN_TIMEOUT_MS to 5s (3s was too aggressive from Vercel)
- Keep FETCH_TIMEOUT_MS at 8s (down from original 20s)

* fix: deploy to Frankfurt, increase timeouts, add retry logic

- Set preferredRegion to 'fra1' (Frankfurt) — closest to OpenSky EU servers
- Increase FETCH_TIMEOUT_MS to 15s and TOKEN_TIMEOUT_MS to 8s
  (OpenSky is slow from cloud IPs, needs more time)
- Add retry logic: 1 retry with 500ms delay before giving up
- Keep safe DOMException handling for Vercel runtime compat

* feat: add Railway proxy for OpenSky API, proxy mode for Vercel route

OpenSky blocks/throttles requests from Vercel's IP ranges. This adds:

1. **Railway proxy** (`proxy/`) — standalone Node.js server that handles
   OpenSky API calls with auth, caching, and CORS. Zero dependencies.

2. **Proxy mode in Vercel route** — when OPENSKY_PROXY_URL env var is set,
   the Vercel /api/flights route forwards requests to the Railway proxy
   instead of calling OpenSky directly.

Setup:
- Deploy proxy/ to Railway with OPENSKY credentials
- Set OPENSKY_PROXY_URL in Vercel to the Railway URL
- Remove OPENSKY credentials from Vercel (only needed on Railway)

* refactor: call OpenSky directly from browser, remove server-side proxy

OpenSky supports CORS (Access-Control-Allow-Origin: *), so we can
call the API directly from the user's browser. This bypasses
Vercel's cloud-provider IPs that OpenSky blocks.

Changes:
- opensky.ts: fetch from opensky-network.org/api directly (was /api/flights)
- use-flights.ts: fix DOMException abort detection
- Remove src/app/api/flights/route.ts (server-side proxy)
- Remove proxy/ directory (Railway proxy)

The app is now fully static — no server-side API routes needed.

* chore: remove server-side API route (now browser-side)

* chore: remove Railway proxy (no longer needed)

* chore: remove proxy package.json

* chore: remove proxy README

* polish: production-grade cleanup, security hardening, remove redundant comments

- Remove redundant JSDoc blocks in opensky.ts, keep only @see link
- Add bounds-clamping for lat/lng parameters (defense-in-depth)
- Fix memory leak: map.on("movestart") listener now cleaned up on unmount
- Validate GA_ID format before interpolating into script tag (XSS defense)
- Remove duplicate canonical <link> tag (already set via metadata.alternates)
- Sanitize JSON-LD output with \u003c escaping to prevent </script> injection
- Use useRef instead of useState for mutable TrailStore class instance
- Fix unused useState import in use-trail-history
- Add Map.displayName for React DevTools
- Fix Tailwind lint: px-[2px] → px-0.5
- Remove unused OPENSKY credentials from .env.example

* chore: push remaining polished files (flight-tracker, use-flights, map)

- flight-tracker: movestart listener cleanup on unmount
- use-flights: clean up redundant comments, fix abort detection
- map: add displayName, remove redundant comment prefix

* chore: polish control-panel (clean comments, Tailwind lint fix)

src/components/ui/control-panel.tsx

@@ -236,7 +236,7 @@ function PanelDialog({
               </a>
               <div className="border-t border-white/3 pt-2 px-2.5">
                 <p className="text-[10px] font-medium text-white/10 tracking-wide">
-                  v0.1 · OpenSky Network
+                  v0.1 \u00b7 OpenSky Network
                 </p>
               </div>
             </div>
@@ -298,7 +298,7 @@ function PanelDialog({
             </div>
           </div>
 
-          {/* Mobile tab bar — at bottom for thumb reach */}
+          {/* Mobile tab bar */}
           <div className="flex sm:hidden items-center gap-1 border-t border-white/6 px-3 pt-2 pb-3">
             <nav className="flex flex-1 gap-1">
               {TABS.map(({ id, icon: Icon, label }) => {
@@ -423,7 +423,7 @@ function SearchContent({
                   {city.name}
                 </p>
                 <p className="text-[11px] font-medium text-white/25">
-                  {city.iata} · {city.country}
+                  {city.iata} \u00b7 {city.country}
                 </p>
               </div>
               <ChevronRight className="h-3.5 w-3.5 shrink-0 text-white/12 transition-colors group-hover:text-white/25" />
@@ -457,7 +457,7 @@ function StyleContent({
       </div>
       <div className="border-t border-white/4 px-5 py-3">
         <p className="text-[11px] font-medium text-white/12">
-          Satellite &copy; Esri · Terrain &copy; OpenTopoMap · Base maps &copy;
+          Satellite \u00a9 Esri \u00b7 Terrain \u00a9 OpenTopoMap \u00b7 Base maps \u00a9
           CARTO
         </p>
       </div>
@@ -632,7 +632,7 @@ function OrbitSpeedSlider({
   const activeLabel =
     ORBIT_SPEED_PRESETS.find(
       (p) => Math.abs(p.value - value) < ORBIT_SNAP_THRESHOLD,
-    )?.label ?? `${value.toFixed(2)}×`;
+    )?.label ?? `${value.toFixed(2)}\u00d7`;
 
   function handleChange(vals: number[]) {
     let raw = vals[0];
@@ -666,7 +666,7 @@ function OrbitSpeedSlider({
             onValueChange={handleChange}
             aria-label="Orbit speed"
           />
-          <div className="pointer-events-none absolute inset-x-0 top-1/2 -translate-y-1/2 flex justify-between px-[2px]">
+          <div className="pointer-events-none absolute inset-x-0 top-1/2 -translate-y-1/2 flex justify-between px-0.5">
             {ORBIT_SPEED_PRESETS.map((preset) => {
               const pct =
                 ((preset.value - ORBIT_SPEED_MIN) /