Drop the last references to the removed hive matrix login form

`PutMatrixAccountRequest`'s no-`Debug` comment named the deleted
`MatrixLoginForm` as its precedent; it now states the reason directly.
The daemon's missing-sidecar warning told operators to re-login via the
dashboard, which no longer has that form; it now points at re-linking
the account from the swarm UI, whose stored credential carries the
homeserver the sidecar is written from. Behaviour is unchanged.

Refs #4348

hive-matrix-mcp/src/accounts.rs

@@ -208,7 +208,7 @@ fn discover_token_accounts_in(
                 account = name,
                 sidecar = %sidecar.display(),
                 "matrix: discovered token but no homeserver sidecar; skipping account \
-                 (re-login via the dashboard to write it)"
+                 (re-link the account from the swarm UI to write it)"
             );
             continue;
         };