feat(tui): add keymap debug inspector

[fcoury-oai]

Why

We constantly get bug reports about keys not being recognized by Codex when the terminal is not handling the key press. Running /keymap debug or /keymap and going to the Debug tab, we can allow the user to either understand that the key being pressed is not being recognized or to check what it's being recognized as and report or reassign that key.

Menu	Inspector	Hint

Summary

• add a Debug tab to /keymap and support /keymap debug for direct access
• show what key Codex receives, the config key representation, raw event details, and matching actions
• add a progressive missing-key hint that escalates after a few seconds with no detected keypress

Validation

• just fmt
• cargo test -p codex-tui keymap_setup::tests::debug_view
• cargo test -p codex-tui keymap_setup::tests
• cargo test -p codex-tui slash_keymap
• cargo test -p codex-tui (unit tests passed; integration test suite::model_availability_nux::resume_startup_does_not_consume_model_availability_nux_count failed locally by itself with codex resume exiting 1 and terminal probe escape output)
• just fix -p codex-tui
• just argument-comment-lint
• cargo insta pending-snapshots
• git diff --check