feat: Complete Unity/game engine support and local source type validation

Completes the implementation for Unity/Unreal/Godot game engine support
and adds missing "local" source type validation.

Changes:
- Add "local" to VALID_SOURCE_TYPES in config_validator.py
- Add _validate_local_source() method with full validation
- Add Unity/Unreal/Godot to FRAMEWORK_MARKERS for priority detection
- Add game engine directory exclusions to all 3 scrapers:
  * Unity: Library/, Temp/, Logs/, UserSettings/, etc.
  * Unreal: Intermediate/, Saved/, DerivedDataCache/
  * Godot: .godot/, .import/
- Prevents scanning massive build cache directories (saves GBs + hours)

This completes all features mentioned in PR #278:
✅ Unity/Unreal/Godot framework detection with priority
✅ Pattern enhancement performance fix (grouped approach)
✅ Game engine directory exclusions
✅ Phase 5 SKILL.md AI enhancement
✅ Local source references copying
✅ "local" source type validation
✅ Config field name compatibility
✅ C# test example extraction

Tested:
- All unified config tests pass (18/18)
- All config validation tests pass (28/28)
- Ready for Unity project testing

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/architectural_pattern_detector.py

@@ -88,6 +88,11 @@ class ArchitecturalPatternDetector:
 
     # Framework detection patterns
     FRAMEWORK_MARKERS = {
+        # Game Engines (checked first to avoid false positives)
+        "Unity": ["Assembly-CSharp", "UnityEngine", "Assets", ".unity", "ProjectSettings"],
+        "Unreal": ["Source/", ".uproject", "Config/DefaultEngine.ini", "Binaries/", "Content/"],
+        "Godot": ["project.godot", ".godot", "scenes/", ".tscn", ".gd"],
+        # Web Frameworks
         "Django": ["django", "manage.py", "settings.py", "urls.py"],
         "Flask": ["flask", "app.py", "wsgi.py"],
         "Spring": ["springframework", "@Controller", "@Service", "@Repository"],