refactor: agents and skills move to a client-neutral source that renders per client

`.claude/agents/` was the source of truth, which made every role Claude-Code
shaped. Adding a second client meant rewriting each role in that client's syntax
and maintaining both copies — the drift this scaffold exists to prevent, one layer
up.

Roles and skills now live under `.agents/` and render into each registered
client. `.claude/agents/`, `.claude/skills/` and `.codex/agents/` are generated;
`scripts/sync-agent-integrations.py --check` fails on drift and belongs in CI.

The role metadata is portable rather than vendor-named: `reasoning_tier`
(deep/balanced/fast/vision), `capabilities`, `mutation`, `invocation`, and an
optional `preload_skills`. A client manifest maps those to native syntax and must
declare what it cannot express — `codex.yaml` declares `tier_policy: unsupported`
and its adapters say so in the file, rather than the tier silently evaporating and
leaving the repository to believe it was enforced.

The port is behaviour-preserving where it should be and a fix where it should not.
Every instruction body is byte-identical — the whole diff to `.claude/agents/` is
18 added lines and zero deletions. What changed is frontmatter that was missing:

- four agents (`code-reviewer`, `tdd-guardian`, `dependency-audit`, `pr-creator`)
  declared no `tools:` and therefore inherited the ENTIRE tool pool, so three
  review-only agents could edit and write the code they were reviewing. All eight
  now declare capabilities explicitly.
- the six read-only roles gain a non-editing permission mode, so the constraint is
  enforced by the client rather than by the prompt asking nicely.
- `mutation` is now explicit, which records the two roles that genuinely need to
  write: `pr-creator` (external-write — it pushes a branch and opens a PR) and
  `dependency-audit` (workspace-write — package managers rewrite lockfiles).

`pr-creator` keeps `shell` because opening a PR needs it, but it is now the only
agent here with a write mutation and a declared reason for it, instead of one of
four with unlimited access by omission.

.claude/agents/code-reviewer.md

@@ -2,7 +2,10 @@
 name: code-reviewer
 description: Comprehensive code review agent covering TDD, type safety, security, patterns, and testing quality. Use before merging PRs or for self-review.
 model: opus
+tools: Read, Grep, Glob, Bash
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/code-reviewer.md; edit the neutral source. -->
 
 # Code Reviewer Agent
 

.claude/agents/dependency-audit.md

@@ -2,7 +2,9 @@
 name: dependency-audit
 description: Audits project dependencies for security vulnerabilities, outdated packages, and license compliance. Use before releases or as part of regular maintenance.
 model: sonnet
+tools: Read, Grep, Glob, Bash
 ---
+<!-- Generated from .agents/roles/dependency-audit.md; edit the neutral source. -->
 
 # Dependency Audit Agent
 

.claude/agents/plan-reviewer.md

@@ -3,7 +3,9 @@ name: plan-reviewer
 description: Read-only validation of implementation plans before work begins. Checks structure, dependencies, scope, and completeness. Use before starting any planned work.
 model: sonnet
 tools: Read, Grep, Glob
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/plan-reviewer.md; edit the neutral source. -->
 
 # Plan Reviewer Agent
 

.claude/agents/pr-creator.md

@@ -2,7 +2,9 @@
 name: pr-creator
 description: Automates branch-to-PR workflow. Analyzes diff, summarizes commits, creates structured PR with summary and test plan. Use when ready to open a pull request.
 model: haiku
+tools: Read, Grep, Glob, Bash
 ---
+<!-- Generated from .agents/roles/pr-creator.md; edit the neutral source. -->
 
 # PR Creator Agent
 

.claude/agents/refactor-scan.md

@@ -3,7 +3,9 @@ name: refactor-scan
 description: Assesses refactoring opportunities after tests pass. Use proactively during TDD's third step (REFACTOR) or reactively to evaluate code quality improvements.
 model: sonnet
 tools: Read, Grep, Glob, Bash
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/refactor-scan.md; edit the neutral source. -->
 
 # Refactor Scan Agent
 

.claude/agents/release-notes.md

@@ -3,7 +3,9 @@ name: release-notes
 description: Generates CHANGELOG entries from git history between two points (tag-to-tag or commit range). Categorizes by Added, Changed, Fixed, Removed. Use before releases.
 model: haiku
 tools: Read, Grep, Glob, Bash
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/release-notes.md; edit the neutral source. -->
 
 # Release Notes Agent
 

.claude/agents/security-scanner.md

@@ -3,7 +3,9 @@ name: security-scanner
 description: Scans code for security vulnerabilities, secrets, and common security anti-patterns. Use before commits or during code review.
 model: sonnet
 tools: Read, Grep, Glob, Bash
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/security-scanner.md; edit the neutral source. -->
 
 # Security Scanner Agent
 

.claude/agents/tdd-guardian.md

@@ -2,7 +2,10 @@
 name: tdd-guardian
 description: Enforces Test-Driven Development compliance. Use proactively when planning code changes and reactively to verify TDD was followed.
 model: sonnet
+tools: Read, Grep, Glob, Bash
+permissionMode: plan
 ---
+<!-- Generated from .agents/roles/tdd-guardian.md; edit the neutral source. -->
 
 # TDD Guardian Agent