feat: initial agent-reviewer meta-agent

A2A agent that audits another deployed agent's source pre-deploy.
Reads the target Gitea repo via a short-lived read-only token minted
through ctx.mint_gitea_token(), runs an inner DeepAgents graph backed
by GiteaBackend, and emits a typed ReviewReport.

Skill bundles:
- security-anti-patterns (credentials, eval, sandbox bypass, egress)
- a2apack-best-practices (class shape, decorators, types, timeouts)
- grant-scope-evaluation (declared vs actual workspace scope)

Tools:
- sandbox_a2a_card  : round-trips the project through microsandbox
- sandbox_ruff_check: objective static checks
- submit_review_report: typed final report

7 smoke tests pass; agent card loads cleanly via `a2a card`.

README.md

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+# agent-reviewer
+
+Pre-deploy audit agent. Reads another agent's source from Gitea, applies
+three skill bundles (security, A2A Pack best practices, grant scope), and
+returns a typed `ReviewReport`.
+
+## Skill: `review`
+
+```
+review(agent_name: str, ref: str = "main", owner: str | None = None) -> ReviewReport
+```
+
+Workflow:
+
+1. Mint a short-lived **read-only** Gitea token via the control plane.
+2. Spin up a DeepAgents graph backed by a `GiteaBackend` pointed at
+   `{owner}/{agent_name}@{ref}`.
+3. Read the source, consult the bundled skills, run sandbox checks
+   (`a2a card`, `ruff`), produce findings.
+4. Release the Gitea token in `finally`.
+
+## Output
+
+`ReviewReport`:
+
+```python
+class Finding(BaseModel):
+    severity: "critical" | "warning" | "info"
+    category: "security" | "correctness" | "ergonomics" | "policy" | "scope"
+    message: str
+    file: str | None
+    line: int | None
+    suggestion: str | None
+
+class ReviewReport(BaseModel):
+    ok: bool                # True iff zero critical findings
+    agent_name: str
+    ref: str
+    summary: str
+    findings: list[Finding]
+```
+
+## Operational notes
+
+- Read-only by design. Never writes to the target repo, never deploys.
+- Uses the `meta-agent-reader` Gitea service user via the platform's
+  `POST /v1/platform/gitea-token` endpoint.
+- Caller must run through the orchestrator (cp_jwt is forwarded).