feat(deploy): derive the API origin from the page, not from a pinned env var

The browser hard-required API_ORIGIN, so every move of the server — tailnet
today, the 192.168.1.0 office LAN later, a temporary demo domain in between —
meant editing the deploy env and redeploying. Worse, an http:// API origin on a
page served over TLS is blocked outright as mixed active content, which is what
broke the demo on https://jorgecuadros.freakma.com.

The browser now derives the origin from window.location the way a PHP app
would: same host on port 3001 over plain HTTP, or the same-origin /api path
under https (the reverse proxy strips the prefix). API_ORIGIN survives as an
optional override for a deployment that genuinely splits the two hosts, and SSR
still reads process.env because a derived origin is browser-only.

WEB_ORIGIN becomes a comma-separated list to match: one deployment is now
reached under several origins, and a credentialed fetch from an unlisted one
gets no CORS headers and fails.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/main.ts

@@ -60,7 +60,19 @@ async function bootstrap() {
   app.use(passport.initialize());
   app.use(passport.session());
 
-  app.enableCors({ credentials: true, origin: process.env.WEB_ORIGIN ?? "http://localhost:3000" });
+  // The same deployment is reached under several origins — the office LAN IP,
+  // the tailnet name, the demo domain — and the browser derives the API origin
+  // from whichever one served the page (apps/web/src/lib/api.ts). So WEB_ORIGIN
+  // is a comma-separated LIST, not a single value. A request whose Origin is
+  // not listed gets no CORS headers and the credentialed fetch fails, so add an
+  // entry when a new way of reaching the app is introduced. Same-origin setups
+  // (web and API behind one proxy) never hit CORS at all.
+  const webOrigins = (process.env.WEB_ORIGIN ?? "http://localhost:3000")
+    .split(",")
+    .map((o) => o.trim())
+    .filter(Boolean);
+
+  app.enableCors({ credentials: true, origin: webOrigins });
 
   const port = process.env.PORT ? Number(process.env.PORT) : 3001;
   await app.listen(port);