fix: address Copilot PR review comments (round 2)

- Fix init --preset error masking: distinguish "not found" from real errors
- Fix bash resolve_template: skip hidden dirs in extensions (match Python/PS)
- Fix temp dir leaks in tests: use temp_dir fixture instead of mkdtemp
- Fix self-test catalog entry: add note that it's local-only (no download_url)
- Fix Windows path issue in resolve_with_source: use Path.relative_to()
- Fix skill restore path: use project's .specify/templates/commands/ not source tree
- Add encoding="utf-8" to all file read/write in agents.py
- Update test to set up core command templates for skill restoration

presets/catalog.json

@@ -5,11 +5,12 @@
   "presets": {
     "self-test": {
       "name": "Self-Test Preset",
-      "description": "A preset that overrides all core templates for testing purposes",
+      "description": "A preset that overrides all core templates for testing purposes. Install with --dev from the repo.",
       "author": "github",
       "version": "1.0.0",
       "repository": "https://github.com/github/spec-kit",
       "license": "MIT",
+      "note": "This preset is bundled with the repo and intended for local testing only. Install via: specify preset add --dev presets/self-test",
       "requires": {
         "speckit_version": ">=0.1.0"
       },