Follow-up to #717. Replaces all remaining hardcoded keybinding hints with configurable ones.
- Add pasteImage to AppAction so it can be configured in keybindings.json
- Create keybinding-hints.ts with reusable helper functions:
- editorKey(action) / appKey(keybindings, action) - get key display string
- keyHint(action, desc) / appKeyHint(kb, action, desc) / rawKeyHint(key, desc) - styled hints
- Export helpers from components/index.ts for extensions
- Update all components to use configured keybindings
- Remove now-unused getDisplayString() from KeybindingsManager and EditorKeybindingsManager
- Use keybindings.matches() instead of matchesKey() for pasteImage in custom-editor.ts
- Add expandTools to EditorAction in pi-tui so components can access it
- Update bash-execution, compaction-summary-message, branch-summary-message,
and tool-execution to use getEditorKeybindings().getKeys('expandTools')
- Pass expandTools config to setEditorKeybindings in KeybindingsManager.create()
- Style keybinding with 'dim' color, description with 'muted' (matches startup hints)
