feat(mcp): let the connector address carry its own key

verdande could not be added to Claude at all. The documented setup —
POST /api/v1/mcp with an Authorization header — cannot be configured from
Claude's custom-connector dialog, which asks for a name, a URL and OAuth
client credentials and has no field for a bearer token. The instructions
described something the interface does not offer.

Worse, the obvious guess failed silently in the most misleading way
available: /mcp was not a route, so the SPA fallback answered 200 with a
page of HTML. The connector reported a successful connection and then
failed to parse the response, which reads as a broken client rather than
a missing endpoint.

So /mcp exists now and takes its credential in the query string, exactly
as the calendar feed does and for the same reason: a client that cannot
be told to send a header means the address is the credential. The
request logger records paths without their query strings, so the key does
not reach the log.

It is deliberately outside /api/v1 and accepts the key and nothing else.
Reading a session cookie here would make it a state-changing POST outside
the CSRF check — a cross-site request that acts as whoever is signed in —
and there is a test that fails if that ever becomes true.

The API path is unchanged for anything that can send a header. The tokens
page now shows the connector address next to the token it belongs to,
since that is the one moment the token exists.

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

docs/openapi.yaml

@@ -1787,6 +1787,53 @@ paths:
       responses:
         "302": { description: "Back into the app, with the outcome as a query parameter." }
 
+  /mcp:
+    post:
+      tags: [integrations]
+      summary: The MCP endpoint, with the token in the query string.
+      description: |
+        The same server as `/api/v1/mcp`, for a client that can only be given a
+        URL. Claude's custom-connector dialog asks for a name, an address and
+        OAuth client credentials — there is no field for a bearer token — so the
+        API path cannot be configured from it.
+
+        The key is the only credential accepted here. A session cookie is
+        ignored: this route sits outside the CSRF check, and honouring a cookie
+        would make it a cross-site request that acts as whoever is signed in.
+      security: []
+      parameters:
+        - name: key
+          in: query
+          required: true
+          schema: { type: string, example: vrd_… }
+          description: A personal API token. Treat the whole address as a password.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [jsonrpc, method]
+              properties:
+                jsonrpc: { type: string, const: "2.0" }
+                id: { oneOf: [{ type: string }, { type: integer }] }
+                method: { type: string }
+                params: { type: object }
+      responses:
+        "200":
+          description: A JSON-RPC response.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  jsonrpc: { type: string, const: "2.0" }
+                  id: { oneOf: [{ type: string }, { type: integer }] }
+                  result: { type: object }
+                  error: { type: object }
+        "202": { description: A notification. No body. }
+        "401": { $ref: "#/components/responses/Unauthorized" }
+
   /.well-known/caldav:
     get:
       tags: [integrations]