bxctl: escape error details, time out on admin.sock, AdminError::Io

M3a review findings 9, 10, 12, 13. A retrying error and every error detail
can carry the inference server's body, so they are escaped like model text.
Admin requests wait at most 30 s, so a stuck brokerd cannot hang bxctl or a
chat turn. A failed write is AdminError::Io and stops handle_pending instead
of being answered with another write. The usage line says what audit verify
checks.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/bxctl/src/cli.rs

@@ -25,7 +25,7 @@ usage: bxctl <command> [options]
       Check that the grants load.
 
   bxctl audit verify [--home DIR]
-      Verify the audit log against the grants.";
+      Check the audit log's hash chain, reading the files directly.";
 
 // The options every `chat` call carries. `socket` is the loop socket; `admin_socket` is the admin
 // socket the other subcommands use. Both default to the paths under `$BOXMAKER_HOME`.