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.

plugins/README.md

@@ -11,11 +11,11 @@ before every edit.
 ## Installation
 
 The framework install/update scripts auto-register this plugin in
-`~/.config/opencode/opencode.jsonc`:
+`~/.config/opencode/opencode.json` (or `opencode.jsonc`):
 
 ```json
 {
-  "plugins": ["~/.automaton/plugins/automaton-guard"]
+  "plugin": ["~/.automaton/plugins/automaton-guard"]
 }
 ```