Add /hooks browser for lifecycle hooks

[abhinav-oai]

Why

This is stacked on #19840.

hooks/list and hooks/config/write make lifecycle hooks inspectable and writable, but there is not yet a first-class TUI surface for users to see what is installed or manage individual handlers when an event has more than one hook. This adds a /hooks flow that makes those hooks discoverable without collapsing multiple handlers into one row, and keeps the interaction model consistent with the existing skills toggle UI (reference).

What

• add a two-page /hooks browser in the TUI: an event overview with installed/active counts, followed by a per-event handler page with toggle controls and detail rendering
• thread plugin identity and managed-state metadata through hook discovery and hooks/list so the UI can label plugin/config sources and suppress toggles for admin-managed hooks
• persist hook toggles through the existing config-write path and add snapshot coverage for the event list, handler list, managed-hook, and empty states

Test Plan

• cargo test -p codex-tui hooks_browser --lib
• cargo test -p codex-hooks
• cargo test -p codex-core-plugins
• cargo test -p codex-app-server-protocol
• cargo test -p codex-app-server --test all v2::hooks_list