feat(dashboard): Overview V2 - Codebase Intelligence

WHAT:
- Replace basic stats with intelligent codebase analysis
- Auto-detect entry points from dependency graph
- Show high-impact files with dependency counts
- Architecture tree with core annotations
- Code health indicators (type coverage, naming consistency)
- Quick actions to navigate between tabs

WHY:
- Competitive differentiation from DeepWiki
- DeepWiki = static documentation
- CodeIntel = actionable intelligence
- Help developers START WORKING, not just READ

COMPONENTS:
- CodebaseIntelligence.tsx: Main intelligence card
- Updated RepoOverview.tsx: Uses new component
- onTabChange prop for cross-tab navigation

Data derived from existing APIs:
- /dependencies: entry points, architecture
- /style-analysis: health metrics
- No backend changes needed

Author: DevanshuNEU