chore(claude): add recce-pr-verifier subagent

[even-wei]

PR checklist

• Ensure you have added or ran the appropriate tests for your PR.
• DCO signed

What type of PR is this?

chore: tooling — adds a Claude Code subagent definition.

What this PR does / why we need it:

Adds .claude/agents/recce-pr-verifier.md, a project-level subagent that encodes the recce repo's PR-verification recipe (uv-based bootstrap, make check, uv run pytest tests, optional frontend pnpm lint && type:check && test, PR hygiene against origin/main).

The team uses many agents to verify PRs. A general-purpose agent burns tokens re-discovering the toolchain (uv vs bare python, which Makefile targets are read-only, where the PR template lives, which gotchas to skip). This subagent is pre-scoped to the repo so a dispatch goes straight to the work.

Encoded gotchas (already in CLAUDE.md / AGENTS.md, now reachable from a single dispatch):

• RecceCloudException does not inherit from RecceException — code wrapping cloud-mode DAO ops with except RecceException will leak; flag missing dual-catch (PR fix(mcp): DRC-3307 fix submit_run race condition + run_check auto-approve #1342, DRC-3307)
• MCP tool description ↔ response shape sync rule (description is the LLM agent contract)
• summary.py row-count None guard for TABLE_NOT_FOUND / PERMISSION_DENIED
• Storybook imports must use @datarecce/ui/components, not relative paths into the package
• CSS color format: space-separated rgb(255 173 21), never legacy rgba(...)
• Cross-repo: when mcp_server.py response format changes, also update recce_instance_launcher/recce_agent/src/recce/agent.ts in recce-cloud-infra

Which issue(s) this PR fixes:

None — internal tooling addition.

Special notes for your reviewer:

Smoke-tested twice end-to-end before opening:

• Round 1 (clean origin/main worktree): PASS. Caught + fixed a main..HEAD vs origin/main..HEAD bug in the original draft (would have produced 33 false-positive "commits ahead" against stale local main).
• Round 2 (feature/drc-3383-recce-gitlab-summary-... — 1 commit, 4 files, net −869 LOC): PASS. The "Do NOT Flag" gotcha rules saved 2 real false positives (RecceCloudException catch pattern + logger.warning level), and the cross-repo MCP description sync check correctly confirmed no follow-up needed in recce-cloud-infra.

The agent never auto-fixes or pushes — it produces a pass/fail report and leaves git operations to the dispatcher.

Does this PR introduce a user-facing change?:

NONE