refactor: adjust agent model assignments based on role analysis

- frontend-architect: opus → sonnet (executes planner's plan)
- backend-architect: opus → sonnet (executes planner's plan)
- code-reviewer: sonnet → opus (deep reasoning for vulnerability/architecture analysis)
- prompt-engineer: marked as optional (only for projects with LLM integration)

Principle: planner does deep thinking, implementation agents execute the plan.
Opus reserved for: planning, security audit, code review.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agents/README.md

@@ -7,27 +7,29 @@ This directory contains specialized AI agent profiles. Each profile defines a ro
 | Agent                | File                      | Model  | Use When                                                 |
 | -------------------- | ------------------------- | ------ | -------------------------------------------------------- |
 | Planner              | `planner.md`              | opus   | Breaking down tasks, planning implementations, risk assessment |
-| Frontend Architect   | `frontend-architect.md`   | opus   | UI components, performance, accessibility, React/Next.js |
-| Backend Architect    | `backend-architect.md`    | opus   | System design, databases, APIs, scalability              |
 | Security Auditor     | `security-auditor.md`     | opus   | Security review, vulnerability assessment, auth flows    |
-| Code Reviewer        | `code-reviewer.md`        | sonnet | Code quality, PR review, best practices                  |
+| Code Reviewer        | `code-reviewer.md`        | opus   | Code quality, PR review, deep analysis                   |
+| Frontend Architect   | `frontend-architect.md`   | sonnet | UI components, performance, accessibility, React/Next.js |
+| Backend Architect    | `backend-architect.md`    | sonnet | System design, databases, APIs, scalability              |
 | Test Engineer        | `test-engineer.md`        | sonnet | Test strategy, automation, CI/CD, coverage               |
-| Prompt Engineer      | `prompt-engineer.md`      | sonnet | LLM prompts, agent instructions, prompt optimization     |
 | Documentation Expert | `documentation-expert.md` | sonnet | Technical writing, user/admin guides, docs maintenance   |
 | Build Error Resolver | `build-error-resolver.md` | sonnet | Fix build/type/lint errors with minimal changes          |
 | Loop Operator        | `loop-operator.md`        | sonnet | Monitor autonomous loops, detect stalls, escalate        |
+| Prompt Engineer *    | `prompt-engineer.md`      | sonnet | LLM prompts, agent instructions (optional, for AI projects) |
 
 ## Model Selection
 
-- **opus** — Deep reasoning tasks: planning, architecture, security review. Slower but more thorough.
-- **sonnet** — Implementation tasks: code review, testing, writing, fixing. Faster turnaround.
+- **opus** — Deep reasoning: planning, security audit, code review. Slower but more thorough.
+- **sonnet** — Implementation: architecture execution, testing, writing, fixing. Faster turnaround.
+
+Principle: planner does the deep thinking, implementation agents execute the plan.
 
 ## Tool Restrictions
 
 Each agent declares a `tools` array in its frontmatter, following the principle of least privilege:
-- **Read-only agents** (planner, architects): Read, Glob, Grep — they advise, not implement
-- **Implementation agents** (test-engineer, build-error-resolver): Read, Glob, Grep, Edit, Write, Bash
-- **Review agents** (code-reviewer): Read, Glob, Grep, Bash (for git commands)
+- **Read-only agents** (planner): Read, Glob, Grep — plans, doesn't implement
+- **Implementation agents** (architects, test-engineer, build-error-resolver): Read, Glob, Grep, Edit, Write, Bash
+- **Review agents** (code-reviewer, security-auditor): Read, Glob, Grep, Bash (for git/scan commands)
 
 ## Agent Selection
 

agents/backend-architect.md

@@ -1,6 +1,6 @@
 ---
 name: backend-architect
-model: opus
+model: sonnet
 tools:
   - Read
   - Glob

agents/code-reviewer.md

@@ -1,6 +1,6 @@
 ---
 name: code-reviewer
-model: sonnet
+model: opus
 tools:
   - Read
   - Glob

agents/frontend-architect.md

@@ -1,6 +1,6 @@
 ---
 name: frontend-architect
-model: opus
+model: sonnet
 tools:
   - Read
   - Glob

agents/prompt-engineer.md

@@ -7,8 +7,9 @@ tools:
   - Grep
   - Write
   - Edit
+optional: true
 description: |
-  Prompt engineering specialist for LLMs. Use when:
+  Optional agent for projects with LLM integration. Use when:
   - Creating system prompts for AI agents
   - Improving existing prompts for better consistency
   - Debugging prompts that produce inconsistent outputs