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/codebase_scraper.py

@@ -124,6 +124,7 @@ FOLDER_CATEGORIES = {
 
 # Default directories to exclude
 DEFAULT_EXCLUDED_DIRS = {
+    # Python/Node
     "node_modules",
     "venv",
     "__pycache__",
@@ -141,10 +142,28 @@ DEFAULT_EXCLUDED_DIRS = {
     ".coverage",
     ".eggs",
     "*.egg-info",
+    # IDE
     ".idea",
     ".vscode",
     ".vs",
     "__pypackages__",
+    # Unity (critical - contains massive build cache)
+    "Library",
+    "Temp",
+    "Logs",
+    "UserSettings",
+    "MemoryCaptures",
+    "Recordings",
+    # Unreal Engine
+    "Intermediate",
+    "Saved",
+    "DerivedDataCache",
+    # Godot
+    ".godot",
+    ".import",
+    # Misc
+    "tmp",
+    ".tmp",
 }