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]>

scripts/package-boundaries.json

@@ -74,6 +74,8 @@
       "server/providers/common/http.js",
       "scripts/google-server-key.mjs",
       "src/data/placeProviderPayloads.js",
+      "server/providers/common/same-site.js",
+      "src/localRequestGate.mjs",
       "src/data/routeSteps.js",
       "src/sources/httpBody.js",
       "src/sources/rateLimit.js"
@@ -287,6 +289,8 @@
       "src/loadingFeedback.js",
       "src/data/installationFeedback.js",
       "src/voice/voiceCost.js",
+      "server/providers/common/same-site.js",
+      "src/localRequestGate.mjs",
       "src/voice/actionSchemas.js",
       "server/providers/openai/toolDescriptions.js",
       "src/sources/rateLimit.js"