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-register-guards/DOC_REVIEW.md

@@ -0,0 +1,16 @@
+# Doc Review: fix-register-guards
+
+## Summary
+Updated 3 documentation files that referenced the old `plugins` key (plural) or only mentioned `.jsonc`.
+
+## Doc Updates Made
+1. **contracts/harness-integration.md** (line 107, 113): Changed `"plugins"` → `"plugin"` (singular), added `.json` as alternative to `.jsonc`.
+2. **plugins/README.md** (line 14, 18): Changed `"plugins"` → `"plugin"` (singular), added `.json` as alternative.
+3. **scripts/register-guards.sh** header comment (line 8): Updated detection comment to mention both `.json` and `.jsonc`.
+
+## Findings
+- The `plugins` (plural) → `plugin` (singular) correction is critical — users following the old docs would add a `plugins` key that OpenCode ignores, resulting in no guard activation.
+- The `.jsonc`-only references were misleading for users with the default `opencode.json` file.
+
+## Verdict
+Docs updated and consistent with the fix.