Add verbose diagnostics for /mcp (#18610)

Fixes #18539.

## Summary
The recent `/mcp` performance work kept the default command fast by
avoiding resource and resource-template inventory probes, but it also
removed useful diagnostics for users trying to confirm MCP server state.

This keeps bare `/mcp` on the fast tools/auth path and adds `/mcp
verbose` for the slower diagnostic view. Verbose mode requests full MCP
server status from the app-server and restores status, resources, and
resource templates in the TUI output.

## Testing
In addition to running automation, I manually tested the feature to
confirm that it works.

codex-rs/tui/src/snapshots/codex_tui__history_cell__tests__mcp_tools_output_from_statuses_renders_verbose_inventory.snap

@@ -0,0 +1,15 @@
+---
+source: tui/src/history_cell.rs
+expression: rendered
+---
+/mcp
+
+🔌  MCP Tools
+
+  • plugin_docs
+    • Status: enabled
+    • Auth: Unsupported
+    • Command: docs-server --stdio
+    • Tools: lookup
+    • Resources: Docs (file:///docs)
+    • Resource templates: Doc Template (file:///docs/{id})