`pi config` ignored `~/.pi/agent/keybindings.json`. `selectConfig()`
never called `setKeybindings()`, so the config selector's
`getKeybindings()` fell back to the default TUI bindings. Remaps such as
`"tui.select.down": ["down", "ctrl+n"]` did nothing there, although they
work in `/settings` and the `--resume` picker.
`selectConfig()` now installs
`KeybindingsManager.create(options.agentDir)` before it builds the UI,
the same way the session picker and startup UI do.
**Testing**
- Added `test/config-selector-keybindings.test.ts`. It runs
`selectConfig()` with a stubbed terminal and component and an agent dir
whose `keybindings.json` remaps `tui.select.up` and `tui.select.down`,
then checks that the active keybindings include `ctrl+p` and `ctrl+n`.
It fails without the change and passes with it.
- Manual check: ran `pi config` in tmux with that `keybindings.json`.
Before the change, Ctrl+N did nothing. After it, Ctrl+N moves the
selection like Down.
- `npm run check` reports only two errors, both missing modules in
`packages/schema/test/bench/candidates.ts`. They occur on `main` without
this change.
Fixes#11651
Requested by @badlogic
Co-authored-by: triagent <triagent@localhost>
