fix: scope uninstall guidance cleanup

[jlitola]

Summary

• scope interactive user guidance cleanup to the selected tools
• preserve shared guidance used by any detected retained tool
• preserve a selected tool's guidance when its MCP removal fails
• keep --yes, project uninstall, and guidance-only cleanup scope-wide

Validation

• bun run plugins:generate
• bun run plugins:check
• bun test — 3283 passed
• bun run typecheck
• bun run lint
• bun run format
• bun run build
• bun run smoke:cli — 18 deterministic unauthenticated steps passed
• bun run smoke:mcp — 7 registration steps passed
• targeted uninstall regressions after review fixes — 3 passed
• internal review and three-round Opus review loop — clean

Authenticated live CLI/MCP smoke reached the backend but the final JSON example request was rate-limited with HTTP 429. No agent-e2e workload currently covers interactive uninstall.