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/SPEC.md

@@ -0,0 +1,21 @@
+# Spec: fix-register-guards
+
+## Problem
+`scripts/register-guards.sh` has three compounding bugs that prevent the OpenCode guard from ever being registered:
+
+1. **Line 23**: Only checks for `opencode.jsonc`, not `opencode.json`. Most users have `opencode.json` (the default), so the guard is never detected.
+2. **Line 34**: Writes to `cfg.setdefault('plugins', [])` (plural `plugins`), but the OpenCode config uses `plugin` (singular). The guard path is added to a key that OpenCode ignores.
+3. **Line 33**: Uses `json.load()` to parse `.jsonc` files, which fails on files with `//` comments.
+
+## Fix
+1. Check for both `~/.config/opencode/opencode.json` and `~/.config/opencode/opencode.jsonc` (prefer `.json` if both exist)
+2. Write to the `plugin` key (singular): `cfg.setdefault('plugin', []).append(source)` — note: must not overwrite existing entries like `opencode-mem`
+3. Strip `//` comments before `json.load()`, or use a JSONC-aware parsing approach
+
+Also update the manual install instructions at line 67 to use `plugin` (singular) instead of `plugins`.
+
+## Acceptance Criteria
+- Running `register-guards.sh` on a machine with `opencode.json` (no `.jsonc`) successfully registers the guard
+- The guard path is added to the `plugin` key (singular), preserving existing entries
+- A `.jsonc` file with `//` comments is parsed without error
+- The manual install hint message uses `plugin` (singular)