Fix 11 automation gaps: dead-end phases, autopilot runtime, guard plugin, status.py bugs, Category 3 audit

- Fix decomposition:approved and human_intervention dead-end phases
- Add scripts/autopilot.py: real drive_all() implementation
- Fix guard plugin: throw Error instead of injecting user messages
- Fix status.py: double continue, _require_state, --list-states
- Add Category 3 (git-based modification) audit
- Add Category 5 (stuck-task detection) audit
- All 206 tests pass

tasks/fix-dead-end-phases/IMPLEMENTATION.md

@@ -0,0 +1,10 @@
+# IMPLEMENTATION.md — Fix Dead-End Phases
+
+## Changes Made
+- `scripts/status.py:91`: Changed `"decomposition:approved": []` to `"decomposition:approved": ["complete"]`
+- `scripts/status.py:103`: Added `"human_intervention": ["referee", "complete"]` to LEGAL_TRANSITIONS
+
+## How It Works
+- Parent tasks at decomposition:approved can now transition to complete (after sub-tasks finish)
+- Human intervention tasks can transition back to referee or to complete
+- Verified both transitions are legal via status.py --transition