feat: VS Code extension — inline metrics overlay

[bntvllnt]

Summary

Build a VS Code extension that shows codebase-intelligence metrics inline — PageRank, blast radius, coupling, tension as CodeLens or gutter decorations.

Motivation

• Every major competitor ships a VS Code extension (CKB, Serena, Brokk, vexp)
• Inline metrics make architectural awareness passive, not active
• Extension can drive adoption — developers discover the tool through the IDE
• Complements MCP (agents) and CLI (CI) as the third distribution channel

Features

1. CodeLens annotations: show PageRank, blast radius on file headers
2. Gutter decorations: color-code lines by complexity/risk
3. Hover info: dependency count, coupling, tension on hover
4. Status bar: current file's risk score
5. Command palette: "Show Hotspots", "Show Dead Exports", "Analyze Forces"
6. Tree view: module structure with cohesion verdicts

Approach

• Use existing CLI --json output as data source
• Extension calls codebase-intelligence <path> file <file> --json for per-file data
• Cache results per git HEAD (invalidate on change)
• Webview panel for graph visualization (optional, stretch goal)

Acceptance Criteria

• Extension published to VS Code Marketplace
• CodeLens shows PageRank + blast radius on open files
• Hover shows full FileMetrics
• Command palette exposes top-level tools
• Caches per git HEAD

Priority

Medium-term — Every competitor has one, but MCP/CLI are higher ROI first.