v0.3.0 - React Frontend & Enhanced Metrics

Major Changes:
- Replaced Observable Framework with Vite + React + shadcn/ui
- Single-page dashboard (all visualizations on one page)
- New backend metrics and API endpoints

Frontend (frontend/):
- Vite + React + TypeScript + Tailwind CSS v4
- shadcn/ui components (Card, Select, Slider, Table)
- D3 visualizations with React useRef pattern
- Custom hooks for API data fetching (useApi.ts)
- TypeScript interfaces for type safety (types.ts)

New Visualizations:
- SectionMatrix: Two-column layout showing which sections appear in which files, shared sections highlighted
- InstructionList: All MUST/NEVER/ALWAYS/SHOULD statements with filtering by type and file
- HistoryTimeline: Git commit history for analyzed files

New Backend Metrics:
- max_hierarchy_depth: Deepest file in hierarchy
- avg_hierarchy_depth: Average depth across files
- total_instruction_count: Count of imperative statements
- avg_verb_density: Action verbs per token

New API Endpoints:
- /api/sankey: Nodes (files + sections) and links for hierarchy visualization
- /api/history: Git log for each analyzed file
- /api/instructions: Extracted imperative statements with type, file, line, context

Existing Visualizations (ported to React):
- Similarity Heatmap
- File Network (circular static layout)
- Chord Diagram
- Treemap
- Circle Packing
- Compression Chart
- Diversity Chart
- Redundancy Candidates List

Build:
- cd frontend && npm run build
- cp -r frontend/dist web/dist
- go build -o bin/ihe ./cmd/ihe

Development:
- Terminal 1: ./bin/ihe <path> AGENTS.md .opencode/skills
- Terminal 2: cd frontend && npm run dev -- --port 3000