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/IMPLEMENTATION.md

@@ -0,0 +1,11 @@
+# Implementation: fix-register-guards
+
+## Changes
+- **scripts/register-guards.sh** (line 22-43): Three fixes:
+  1. **Config detection**: Now checks both `opencode.json` (default) and `opencode.jsonc`, preferring `.json` if both exist. Previously only checked `.jsonc`.
+  2. **Config key**: Writes to `plugin` (singular) via `cfg.setdefault('plugin', [])`. Previously wrote to `plugins` (plural) which OpenCode ignores.
+  3. **JSONC parsing**: Strips `//` comments before `json.loads()` using `re.sub(r'//.*?$', '', text)`. Previously used `json.load()` directly which fails on JSONC files with comments.
+- **scripts/register-guards.sh** (line 67): Updated manual install hint to use `plugin` (singular) instead of `plugins`.
+
+## Notes
+- No test added (shell script with external dependencies on `~/.config/opencode/`). Verified manually: `bash -n scripts/register-guards.sh` passes syntax check. The JSONC comment-stripping regex was validated separately.