feat: implement three-mode UI system (Easy / Pro / Chat)
Add switchable UI modes with conditional rendering:
- Easy mode: goal-based interface with 7 guided workflows
- Pro mode: current technical interface preserved with Quick Start Goals
- Chat mode: AIUI placeholder for future integration
New components: ModeSwitcher, EasyHome, GoalDetail wizard, Chat placeholder
New stores: uiMode (mode persistence), goals (progress tracking)
New data: goal definitions catalog, helpTree goals section
Modified: Dashboard (reactive nav), Home (mode dispatcher), Settings (mode picker),
Router (goal/chat routes), Spotlight (goal search integration)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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