chore: add multi-agent build pipeline (.claude/ agents, orchestrator, gates)

Adds crewli-architect, backend/frontend-implementer, test-writer subagents,
the /build-module orchestrator command, the PR merge-gate template, and a
permissions allow-list in settings.json. Documents the layer as
CLAUDE_CODE_TOOLING.md section 10. Implementer Edit/Write is allow-listed;
git push deliberately omitted so merge/push stay human.

Co-Authored-By: Claude <noreply@anthropic.com>

dev-docs/CLAUDE_CODE_TOOLING.md

@@ -190,3 +190,84 @@ the worst of both worlds (the agent reads the rule, the hook fires
 the rule, and when they diverge nobody knows which is right).
 CLAUDE.md is for understanding the project; `.claude/` is for
 catching the mistakes that happen anyway.
+
+## 10. Multi-agent build pipeline
+
+The `.claude/` layer now includes an orchestrated build pipeline on top
+of the deterministic hooks and the review subagent. It automates the
+work Bert previously did by hand (prompt authoring, dispatch, gate
+assembly) while keeping the two irreversible decisions human.
+
+### 10.1 Validated against
+
+- Claude Code version: **<fill in `claude --version` at setup>**
+- Re-verify after every `claude update`: the Agent-tool name, the
+  `isolation: worktree` field, and the subagent permission model have
+  all shifted in point releases. After an update, re-run the §6 hook
+  smoke-tests and one architect dry-run before trusting the chain.
+
+### 10.2 The agents
+
+| Agent | Model | Tools | Role |
+|---|---|---|---|
+| `crewli-architect` | opus | Read, Grep, Glob, Bash | Drift-check, audit, decompose, emit DECISION BRIEF. Plans only — never writes code. |
+| `backend-implementer` | sonnet | + Edit, Write (worktree) | One bounded backend subtask per the approved plan. |
+| `frontend-implementer` | sonnet | + Edit, Write (worktree) | One bounded `apps/app/` subtask. |
+| `test-writer` | sonnet | + Edit, Write (worktree) | PHPUnit + Vitest tests; never weakens a test to pass. |
+| `crewli-reviewer` | opus | Read, Grep, Glob (read-only) | Zero-compromise review; emits `REVIEW VERDICT: PASS\|BLOCK`. |
+
+Implementer prompts are deliberately thin: they encode only what an
+agent would get WRONG without the instruction, and lean on CLAUDE.md +
+SCHEMA.md for the rest. They do NOT duplicate hookable rules (pint,
+eslint, protect-files, block-dangerous-bash already fire on every tool
+call). This is the §1 binding principle applied to agents.
+
+### 10.3 The orchestrator
+
+`/build-module <task>` runs in the MAIN session (subagents can't spawn
+subagents). Five phases:
+
+0. Branch off main (always Phase 0).
+1. Architect -> DECISION BRIEF -> **HUMAN GATE 1** (approve/adjust/reject).
+2. Dispatch implementers + test-writer in dependency order; parallel-
+   safe subtasks run as background subagents with worktree isolation.
+3. Reviewer gate; BLOCK loops back to the implementer without bothering
+   the human; PASS proceeds.
+4. Assemble `pr-merge-gate.md` with real signals -> **HUMAN GATE 2**
+   (reply `merge`). A red signal never reaches the human.
+5. Post-merge: sync-docs reminder; branch cleanup ONLY after merge
+   verification (the D1 near-miss rule).
+
+### 10.4 The two human gates
+
+Both gates are designed to reduce to a single glance + one word:
+
+- **Gate 1** (decomposition): the architect surfaces its own risk flags
+  and open questions at the top of the brief, so Bert weighs only the
+  flagged points, not the whole plan. Reply `approve`.
+- **Gate 2** (merge): every signal is pre-verified green before the gate
+  is shown; a red signal returns the PR to the implementer instead.
+  Bert performs the `--no-ff` merge + push manually. Reply `merge`.
+
+`git push` is intentionally OFF the settings.json allow-list, so the
+"merge & push stay human" rule is enforced at the permission layer.
+
+### 10.5 Permissions interaction
+
+Subagents can't answer "ask" prompts (an asked tool is auto-denied), so
+implementer Edit/Write/Bash are allow-listed in settings.json §permissions.
+The PreToolUse hooks still fire and block the dangerous subset. Allow
+broadly; block narrowly via hooks. Never add `git push` to the allow-list.
+
+### 10.6 Files
+
+```
+.claude/agents/crewli-architect.md
+.claude/agents/backend-implementer.md
+.claude/agents/frontend-implementer.md
+.claude/agents/test-writer.md
+.claude/agents/crewli-reviewer.md        (existing + verdict-line block)
+.claude/commands/build-module.md
+.claude/templates/pr-merge-gate.md
+.claude/settings.json                    (existing hooks + new permissions)
+```