Implement comprehensive keyboard shortcut system for SHIM

Build a fully configurable keyboard navigation system that allows users to: 1. Navigate all modals and entity creation flows via keyboard 2. Jump to different sections of the app 3. Access features like bug list, etc. 4. Configure custom keyboard shortcuts in settings 5. Settings UI: click action → modal appears → press desired key combo → submit 6. Real-time conflict detection showing if shortcut is already assigned 7. Option to reassign shortcuts (taking over from existing action, setting old action to 'no shortcut') 8. Persist all shortcut configurations to local JSON file Scope: Make everything currently doable with mouse also doable with keyboard shortcuts.