feat(archetypes): add comprehensive agent archetype system

- Rename coder.json to engineer.json with enhanced 300+ line system prompt
- Add reviewer.json for code review specialist
- Add tester.json for test engineer
- Add investigator.json for debugging/investigation
- Add shipper.json for release/deployment
- Update architect.json with detailed workflow phases

Each archetype includes:
- Role definition and capabilities
- Workflow phases with specific actions
- Handoff protocols
- Example interactions

.beads/archetypes/coder.json

@@ -1,15 +0,0 @@
-{
-  "id": "coder",
-  "name": "Implementation Engineer",
-  "description": "Translates plans into precise, type-safe, and tested code.",
-  "systemPrompt": "You are a senior software engineer focused on execution and clean code.",
-  "capabilities": [
-    "coding",
-    "refactoring",
-    "testing"
-  ],
-  "color": "#10b981",
-  "createdAt": "2026-02-21T19:37:55.262Z",
-  "updatedAt": "2026-02-21T19:37:55.262Z",
-  "isBuiltIn": true
-}

.beads/archetypes/test-agent.json

@@ -1,14 +0,0 @@
-{
-  "id": "test-agent",
-  "name": "Test Agent",
-  "description": "A test archetype for verification",
-  "systemPrompt": "You are a test agent.",
-  "capabilities": [
-    "testing",
-    "verification"
-  ],
-  "color": "#ff6b6b",
-  "createdAt": "2026-02-21T20:43:00.085Z",
-  "updatedAt": "2026-02-21T20:43:00.085Z",
-  "isBuiltIn": false
-}