feat(install): add CodeBuddy Code CLI platform support

[chuckiefan]

Summary

Adds codebuddy as a new platform to code-review-graph install --platform <name>, supporting the CodeBuddy Code CLI (Tencent's Claude Code–style terminal tool). The IDE product form is intentionally out of scope — it has no file-system config entry point.

Running code-review-graph install --platform codebuddy now produces:

• <repo>/.mcp.json — MCP server entry (shared with claude; format is identical)
• <repo>/CODEBUDDY.md — startup instructions (reuses _CLAUDE_MD_SECTION)
• <repo>/.codebuddy/skills/<slug>/SKILL.md — 4 skills (explore / review / debug / refactor)
• <repo>/.codebuddy/settings.json — PostToolUse + SessionStart hooks (same schema as Claude)

Implementation notes

• Data-driven extension. codebuddy added to PLATFORMS and _PLATFORM_INSTRUCTION_FILES; no special-case branching in install loop.
• Refactor: _merge_hooks_into_settings extraction. Pulled backup + dedup-merge + write logic out of install_hooks (Claude) so install_codebuddy_hooks can reuse it. External API install_hooks(repo_root, platform="claude") -> None unchanged; 53 hooks regression tests pass.
• Dedup in install_platform_configs. Since claude and codebuddy share <repo>/.mcp.json, --platform all previously wrote the file twice. Now the first platform wins the physical write; all sharing platforms are credited in configured.
• Out of scope. User-level ~/.codebuddy/settings.json (enabledMcpjsonServers) is not auto-written — it affects every project.

Design & plan

• Spec: docs/superpowers/specs/2026-06-25-codebuddy-platform-support-design.md
• Plan: docs/superpowers/plans/2026-06-25-codebuddy-platform-support.md

Test plan

• uv run pytest tests/ — 1293 passed, 1 skipped, 2 xpassed (no regressions)
• uv run ruff check code_review_graph/ — clean
• uv run mypy code_review_graph/ — clean (60 source files)
• Manual smoke test: install --platform codebuddy produces all 4 expected artifacts
• Manual dedup test: install --platform all writes .mcp.json exactly once while crediting both Claude Code and CodeBuddy Code
• Per-task TDD reviews all approved (6 commits, base 0c9a5ff..head 09270d4)

[itxaiohanglover]

Clean addition! CodeBuddy support follows the existing platform install pattern. The skills and hooks installation matches the structure used for other platforms.