fix(server): gate cost/log endpoints against cross-site requests and ship a full CSP

The cost-bearing endpoints (/api/realtime/token, /api/openai/hud-summary,
/api/google/nearby-places) and the voice debug log refuse cross-site browser
requests: a foreign or opaque Origin, a Sec-Fetch-Site other than
same-origin/none, or proxy forwarding headers. Loopback tools without an
Origin and the LAN opt-in keep working. The dev and preview servers send one
shared Content-Security-Policy, and embed-mode framing rewrites only the
frame-ancestors directive of it.

Salvaged from #242 onto current main.

Co-authored-by: Sameh Khamis <[email protected]>
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

server/providers/openai.js

@@ -2,6 +2,7 @@ import { defaultSourceRoot } from './common/source-root.js';
 import { handleHudSummary } from './openai/hud-summary.js';
 import { createDebugLogHandler } from './openai/debug-log.js';
 import { createRealtimeTokenHandler } from './openai/realtime.js';
+import { sameSiteGated } from './common/same-site.js';
 
 /**
  * Vite plugin: OpenAI Realtime ephemeral client secret.
@@ -15,16 +16,20 @@ function openAiRealtimeProxy({
   realtime = {},
 } = {}) {
   function install(middlewares) {
-    middlewares.use('/api/openai/hud-summary', handleHudSummary);
+    // Cost-bearing and log endpoints refuse cross-site browser requests
+    // (see server/providers/common/same-site.js and SECURITY.md).
+    middlewares.use('/api/openai/hud-summary', sameSiteGated(handleHudSummary));
 
     middlewares.use(
       '/api/realtime/debug-log',
-      createDebugLogHandler({ sourceRoot }),
+      sameSiteGated(createDebugLogHandler({ sourceRoot })),
     );
 
     middlewares.use(
       '/api/realtime/token',
-      createRealtimeTokenHandler({ ...realtime, annotationGuidance }),
+      sameSiteGated(
+        createRealtimeTokenHandler({ ...realtime, annotationGuidance }),
+      ),
     );
   }