feat: merge four-opencode-git-tools analytics into supertools

[four-bytes-robby]

Purpose

Merge the 5 git-history risk analytics tools from ~/four-opencode-git-tools into supertools. The git-tools project is 3 commits old with zero implementation — just stubs. Merging now avoids maintaining two separate plugins for what should be one coherent "supertools" product.

Tools to Merge

Tool	Description
curse_score	Rank files by risk (changes × author chaos × recency × churn)
bus_factor	Ownership concentration — which modules would be orphaned?
implicit_coupling	Files that always change together (hidden co-commit dependencies)
ownership	Who owns the lines alive in HEAD (per-file/directory breakdown)
blast_radius	When you touch a file, what else might break?

Implementation Steps

1. Create src/tools/curse-score.ts, bus-factor.ts, implicit-coupling.ts, ownership.ts, blast-radius.ts with stub implementations (extracted from the git-tools entry file)
2. Register all 5 tools in src/four-opencode-supertools.ts alongside the existing 4
3. Move/merge test files from git-tools tests/ into supertools tests/
4. Move/merge debug-logger (both projects have one — keep supertools version)
5. Update ROADMAP.md: add Wave S4 "Git Intelligence" with these 5 tools + the planned git_diff_staged, renumber old S4→S5, S5→S6
6. Update README.md tool reference table
7. Update CONTRIBUTING.md if needed
8. Bump version to 0.3.0
9. Run all tests (existing 31 + new ones), typecheck, lint

Acceptance Criteria

• All 9 tools registered: apply_patch, batch_edit, lint_file, run_tests, curse_score, bus_factor, implicit_coupling, ownership, blast_radius
• All 31 existing tests still pass
• New smoke tests for the 5 git tools pass
• ROADMAP.md updated with S4 Git Intelligence wave
• bun run build && bun run typecheck && bun run lint pass