fix(automation): TCP automation requires a session token

--http (headless and GUI-hosted) and --serve --port answered anything
that reached the loopback port, and the REST responses allowed every
web origin. Loopback is shared by every process and user on the
machine, so the port proved nothing.

- Every REST request now needs Authorization: Bearer <token>, and every
  --serve --port request line a "token" field; otherwise 401 /
  unauthorized (the socket is closed).
- The token is OCS_API_TOKEN when the launcher sets it, else 32 random
  bytes printed on stderr at startup; compared in constant time.
- No CORS headers are sent, so a web page cannot read an answer.
- stdio --serve and --mcp are unchanged (private to their parent / the
  GUI's own token).

GHSA-c27p-xfx2-9r5x

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/rest_openapi.json

@@ -6,6 +6,7 @@
     "description": "REST surface over the OpenCAD Studio automation dispatcher. The server runs headless via `OpenCADStudio --http <port>`, binds 127.0.0.1 only, and keeps one drawing session alive across requests. All bodies are JSON; failure bodies carry a symbolic `code` (see the automation README for the catalogue)."
   },
   "servers": [{"url": "http://127.0.0.1:8090"}],
+  "security": [{"bearer": []}],
   "paths": {
     "/api/v1/ready": {
       "get": {
@@ -255,5 +256,10 @@
         "responses": {"200": {"description": "Operation response"}}
       }
     }
+  },
+  "components": {
+    "securitySchemes": {
+      "bearer": {"type": "http", "scheme": "bearer", "description": "OCS_API_TOKEN, or the token printed on stderr at startup."}
+    }
   }
 }