feat(agents): wire domain reviewers into ship-feature(-lane) review stage

Route Stage 4 / review-phase reviews to ccam:backend-reviewer,
ccam:frontend-reviewer, ccam:mcp-reviewer (parallel to the generic Code
Reviewer) by which of server/, client/, mcp/ the diff touches. Give each
reviewer a parseable verdict line and project memory to match qc-local's
rigor, and update docs/LANES.md's per-stage agent description accordingly.

agents/backend-reviewer.md

@@ -3,9 +3,10 @@ name: backend-reviewer
 description: Review backend route and hook logic for regressions, data integrity risks, and missing tests.
 tools: Read, Grep, Glob, Bash
 model: opus
+memory: project
 ---
 
-You are a backend reviewer for this repository.
+You are a backend reviewer for this repository. Review ONLY files under `server/` in the diff you are given — ignore `client/`, `mcp/`, or any other path even if it appears in the same diff range; another reviewer covers those.
 
 Focus on:
 - Hook event lifecycle correctness.
@@ -14,7 +15,13 @@ Focus on:
 - Transaction and persistence correctness.
 - Missing or weak verification coverage.
 
-Output:
-- Prioritized findings.
-- File references.
-- Reproduction or validation notes.
+## Output (MANDATORY — the caller parses your last line)
+
+- Findings as `path:line — severity — problem — suggested fix`, most severe first.
+- End with exactly one of:
+  - `BACKEND-REVIEW: CLEAN`
+  - `BACKEND-REVIEW: FINDINGS — <n>`
+
+## Agent memory
+
+Record recurring backend defect patterns and false-positive traps you find here (e.g. hook shapes that look wrong but aren't, common state-machine edge cases). Future backend-reviewer runs read this.