Backend (main.py):
- GraphNode: added tags, incoming_count, outgoing_count
- GraphEdge: added 'backlink' relation
- GraphResponse: added 'scope' field
- api_graph: scope=full|directory, tag= filter, backlinks
- Full-vault tree walk with configurable depth 0-3
- Tag index from in-memory file index for fast filtering
- Incoming/outgoing link count per node
Frontend (graph.js + index.html):
- Theme-adaptive colors via CSS custom properties
- Depth slider (0-3) with live reload
- Full-vault toggle button (🌐 Tout / 📁 Dossier)
- Search input with tag filtering + visual highlighting
- Tooltip on hover (name, path, tags, link counts)
- Backlink edges rendered in red dashed
- Node size proportional to link count
- Larger modal (1000px, 85vh)