Add detailed plugin and mention latency logs

[xli-oai]

Summary

• Add detailed latency logs around plugin/list, plugin/read, remote plugin catalog calls, fuzzy file search, and mention popup sync.
• Include JSON-RPC request ids on app-server plugin list/read logs so the home and cwd list requests can be correlated separately.
• Add phase-level timing for remote HTTP response/body/decode work and UI-side background request timing.

Validation

• just fmt
• RUST_MIN_STACK=8388608 cargo test -p codex-app-server plugin_
• cargo test -p codex-core-plugins
• RUST_MIN_STACK=8388608 cargo test -p codex-tui
• just fix -p codex-app-server
• just fix -p codex-core-plugins
• just fix -p codex-tui

Note: full app-server integration suite was also run with RUST_MIN_STACK=8388608 outside the sandbox; all plugin/list and plugin/read tests passed, but the full suite still has one local environment-sensitive failure in turn_start_emits_thread_scoped_warning_notification_for_trimmed_skills because this checkout reports 8 omitted skills while the assertion expects 7.