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/prompts/reviewer-acceptance.md

@@ -0,0 +1,22 @@
+# Acceptance Tester Prompt Baseline
+
+Goal:
+- verify the feature or fix is implemented exactly as requested
+
+Input:
+- code diff
+- `plan.json`
+- `execution-report.json`
+
+Required references:
+- `.agents/checks/acceptance-checklist.md`
+
+Output:
+- valid JSON by `.agents/contracts/reviewer-acceptance.schema.json`
+
+Rules:
+- evaluate each `plan.json` success criterion by its `SC-*` ID
+- include evidence for pass/fail checks
+- return `checked_criterion_ids` and per-check `criterion_id` values that match the plan
+- list missing behavior explicitly when verdict is `fail`
+- verify no out-of-scope changes were silently introduced