refactor: relocate agent-system/ to .agents/ with 7-role workflow restructure

Moves the agent workflow system from agent-system/ to .agents/ (dotfile convention).
Restructured from 5-role to 7-role pipeline: adds Analyst and splits Reviewer into
Code Reviewer + Security Reviewer. Removes all old workflow run artifacts.

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

.agents/templates/plan.template.json

@@ -0,0 +1,50 @@
+{
+  "task_id": "TASK-0001",
+  "analysis_ref": ".agents/runs/TASK-0001/analysis.json",
+  "summary": "Short summary of issue or feature",
+  "assumptions": [],
+  "scope": {
+    "in": [],
+    "out": []
+  },
+  "guardrails": {
+    "required_guard_ids": [
+      "GR-CORE-003",
+      "GR-TEST-001",
+      "GR-SEC-008"
+    ],
+    "required_quality_gate_ids": [
+      "QG-001",
+      "QG-002",
+      "QG-003"
+    ]
+  },
+  "success_criteria": [
+    {
+      "id": "SC-001",
+      "criterion": "Measurable acceptance criterion."
+    }
+  ],
+  "implementation_steps": [
+    {
+      "id": "S1",
+      "title": "Step title",
+      "description": "Step detail",
+      "guard_refs": [
+        "GR-CORE-003"
+      ]
+    }
+  ],
+  "tests": [
+    "Test name or PHPUnit class that proves the feature works"
+  ],
+  "acceptance_checks": [
+    "SC-001: Verifiable acceptance step for criterion SC-001"
+  ],
+  "risks": [
+    {
+      "risk": "Risk description",
+      "mitigation": "Mitigation description"
+    }
+  ]
+}