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/github_scraper.py

@@ -53,25 +53,49 @@ except ImportError:
 
 # Directories to exclude from local repository analysis
 EXCLUDED_DIRS = {
+    # Virtual environments
     "venv",
     "env",
     ".venv",
-    ".env",  # Virtual environments
+    ".env",
+    # Dependencies and caches
     "node_modules",
     "__pycache__",
-    ".pytest_cache",  # Dependencies and caches
+    ".pytest_cache",
+    # Version control
     ".git",
     ".svn",
-    ".hg",  # Version control
+    ".hg",
+    # Build artifacts
     "build",
     "dist",
-    "*.egg-info",  # Build artifacts
+    "*.egg-info",
+    # Coverage reports
     "htmlcov",
-    ".coverage",  # Coverage reports
+    ".coverage",
+    # Testing environments
     ".tox",
-    ".nox",  # Testing environments
+    ".nox",
+    # Linter caches
     ".mypy_cache",
-    ".ruff_cache",  # Linter caches
+    ".ruff_cache",
+    # Unity (critical - contains massive build cache)
+    "Library",
+    "Temp",
+    "Logs",
+    "UserSettings",
+    "MemoryCaptures",
+    "Recordings",
+    # Unreal Engine
+    "Intermediate",
+    "Saved",
+    "DerivedDataCache",
+    # Godot
+    ".godot",
+    ".import",
+    # Misc
+    "tmp",
+    ".tmp",
 }