- Update turbovault-parser from 1.2.1 to 1.2.3
- Cleans up transitive dependencies (removes anyhow, nom 7.x, thiserror)
- Bump rust-version to 1.90

- Add keybinds-rs for extensible keybinding dispatch with multi-key sequences
- Add strum for enum iteration and string conversion
- Create keybindings module with Action enum defining all bindable actions
- Add KeybindingMode enum for mode-based keybinding organization
- Add Keybindings struct wrapping keybinds-rs with mode support
- Define comprehensive default keybindings for all modes
- Support TOML configuration format for user customization

Modes supported:
- Normal: main navigation and actions
- Help: help popup scrolling
- ThemePicker: theme selection
- Interactive: element navigation
- InteractiveTable: table cell navigation
- LinkFollow: link navigation and selection
- LinkSearch: link filtering
- Search: outline filtering
- DocSearch: document content search
- CommandPalette: command execution
- CellEdit: table cell editing
- ConfirmDialog: confirmation prompts

- Add keybindings field to Config for TOML-based customization
- Add keybindings() method to Config for loading user bindings
- Add keybindings field to App struct
- Add current_keybinding_mode() to map AppMode to KeybindingMode
- Add get_action_for_key() for action-based key dispatch
- Support all app modes: Normal, Interactive, LinkFollow, Search,
  DocSearch, CommandPalette, Help, ThemePicker, CellEdit, ConfirmDialog

Major refactor of the event loop to use the keybindings system:

- Add ActionResult enum for action outcomes (Continue, Quit, RunEditor)
- Add execute_action() method to App that handles all 60+ actions
- Add helper methods: exit_current_mode(), handle_confirm_action(),
  handle_cancel_action(), handle_search_backspace(), table_navigate_*()
- Replace 600+ lines of nested match statements with clean dispatch
- Separate text input handling from action handling
- Keep character input for search/edit modes outside action system

The event loop is now ~100 lines vs ~600 lines previously, making it
much easier to understand and maintain. All key handling now flows
through the customizable keybindings system.

- JumpToParent now works in both Outline and Content focus
- PageDown/PageUp now properly scroll help popup when in Help mode
- Add scroll_help_page_down/up methods for half-page scrolling

Feature/keybindings v2