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/SPEC.md

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+# Fix Dead-End Phases
+
+## Problem
+- `decomposition:approved` has `[]` in LEGAL_TRANSITIONS (status.py:91). Parent tasks stuck forever.
+- `human_intervention` not in LEGAL_TRANSITIONS at all. Referee can transition into it but never out.
+
+## Fix
+1. Add `decomposition:approved → [complete]` to LEGAL_TRANSITIONS (parent task completes when all subtasks done)
+2. Add `human_intervention → [referee, complete]` to LEGAL_TRANSITIONS (user can send back to referee or mark complete)
+
+## Verification
+- `status.py --transition complete --task <t> --project .` on a decomposition:approved task should succeed
+- `status.py --transition referee --task <t> --project .` on a human_intervention task should succeed