Make revoking an agent and locking a dashboard actually revoke and lock

An MCP access token is a stateless JWT good until it expires, so deleting
the client row revoked nothing already handed out — on the MCP endpoint or
on the REST API, which takes the same token directly. Both doors now look
the client up by the `client_id` the token has always carried, so tokens
already in circulation are held to it too.

A dashboard's `locked` setting stopped the client drawing a control and
nothing else; the server took a publish from a panel showing it anyway. It
now bounds the panel's write scope, resolved live where a flow drives the
flag, exactly as the client resolves it. Reads are untouched — read-only is
not blind — and so is a querying chart's request, which is how that tile
reads rather than something anyone touched.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CL9zvnnvcp1mvA8o7impxk

backend/tests/api/routes/test_oauth.py

@@ -270,6 +270,17 @@ def test_one_agent_can_be_revoked_without_touching_the_others(
     assert revoked.status_code == 200, revoked.text
     assert all(c["id"] != client_id for c in listed())
 
+    # And the access token already in its hands stops working, rather than
+    # outliving the revocation by up to MCP_TOKEN_EXPIRE_MINUTES: the token is
+    # stateless, so the client row it names is what withdrawing it removes.
+    assert (
+        client.post(
+            f"{settings.API_V1_STR}/login/test-token",
+            headers={"Authorization": f"Bearer {tokens['access_token']}"},
+        ).status_code
+        == 401
+    )
+
     # Its refresh token went with it, so it cannot mint itself a new one.
     refreshed = client.post(
         f"{PREFIX}/token",