Fix 10 audit bugs: path prefix matching, verdict parsing, CORS, stale-task detection, phase mapping

Batch 1 (High severity):
- Bug 1: --audit cat3 now checks .automaton/tasks/ paths
- Bug 4: Verdict PASS/FAIL uses structured ## Status: line parsing
- Bug 5: register-guards.sh checks .json/.jsonc, writes plugin key, strips comments
- Bug 7: --can-edit/--scope-check path prefix uses os.sep boundary

Batch 2 (Medium/Low severity):
- Bug 2: migrate-project.sh find command parentheses for -prune binding
- Bug 3: vram_detect model prefix matching with known-suffix whitelist
- Bug 6: dashboard reads .state file before artifact heuristic fallback
- Bug 8: removed wildcard CORS, added security headers (nosniff, DENY)
- Bug 9: stale-task detection uses .state.lastedit instead of .state mtime
- Bug 10: TEST_PLAN.md maps to test_design (was implement)

249 tests pass (up from 235). All 10 tasks driven through full workflow to completion.

tasks/fix-test-plan-phase-mapping/SPEC.md

@@ -0,0 +1,13 @@
+# Spec: fix-test-plan-phase-mapping
+
+## Problem
+`scripts/status.py:344` (`_infer_state_from_artifacts`) maps `TEST_PLAN.md` (without `IMPLEMENTATION.md`) to `"implement"`. But `TEST_PLAN.md` is the artifact of the `test_design` phase. The dashboard's `task.py:510-511` has the same mapping.
+
+## Fix
+Map `TEST_PLAN.md` (without `IMPLEMENTATION.md`) to `"test_design"` in both `status.py:_infer_state_from_artifacts()` and `automaton/dashboard/core/task.py:determine_task_state()`.
+
+## Acceptance Criteria
+- A task with SPEC.md + TEST_PLAN.md (no IMPLEMENTATION.md) infers as `test_design`, not `implement`
+- A task with IMPLEMENTATION.md still infers as `implement`/`code_review`
+- Existing tests still pass
+- Add test for the TEST_PLAN-only case