feat: C3.5 - Architectural Overview & Skill Integrator

Implements comprehensive integration of ALL C3.x codebase analysis features
into unified skills, transforming basic GitHub scraping into comprehensive
codebase intelligence with architectural insights.

**What C3.5 Does:**
- Generates comprehensive ARCHITECTURE.md with 8 sections
- Integrates ALL C3.x outputs (patterns, examples, guides, configs, architecture)
- Defaults to ON for GitHub sources with local_repo_path
- Adds --skip-codebase-analysis CLI flag

**ARCHITECTURE.md Sections:**
1. Overview - Project description
2. Architectural Patterns (C3.7) - MVC, MVVM, Clean Architecture, etc.
3. Technology Stack - Frameworks, libraries, languages
4. Design Patterns (C3.1) - Factory, Singleton, Observer, etc.
5. Configuration Overview (C3.4) - Config files with security warnings
6. Common Workflows (C3.3) - How-to guides summary
7. Usage Examples (C3.2) - Test examples statistics
8. Entry Points & Directory Structure - File organization

**Directory Structure:**
output/{name}/references/codebase_analysis/
├── ARCHITECTURE.md (main deliverable)
├── patterns/ (C3.1 design patterns)
├── examples/ (C3.2 test examples)
├── guides/ (C3.3 how-to tutorials)
├── configuration/ (C3.4 config patterns)
└── architecture_details/ (C3.7 architectural patterns)

**Key Features:**
- Default ON: enable_codebase_analysis=true when local_repo_path exists
- CLI flag: --skip-codebase-analysis to disable
- Enhanced SKILL.md with Architecture & Code Analysis summary
- Graceful degradation on C3.x failures
- New config properties: enable_codebase_analysis, ai_mode

**Changes:**
- unified_scraper.py: Added _run_c3_analysis(), modified _scrape_github(), CLI flag
- unified_skill_builder.py: Added 7 methods for C3.x generation + SKILL.md enhancement
- config_validator.py: Added validation for C3.x properties
- Updated 5 configs: react, django, fastapi, godot, svelte-cli
- Added 9 integration tests in test_c3_integration.py
- Updated CHANGELOG.md with complete C3.5 documentation

**Related:**
- Closes #75
- Creates #238 (type: "local" support - separate task)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/skill_seekers/cli/config_validator.py

@@ -33,6 +33,9 @@ class ConfigValidator:
     # Valid code analysis depth levels
     VALID_DEPTH_LEVELS = {'surface', 'deep', 'full'}
 
+    # Valid AI modes for C3.x enhancement
+    VALID_AI_MODES = {'auto', 'api', 'local', 'none'}
+
     def __init__(self, config_or_path: Union[Dict[str, Any], str]):
         """
         Initialize validator with config dict or file path.
@@ -178,6 +181,19 @@ class ConfigValidator:
         if 'max_issues' in source and not isinstance(source['max_issues'], int):
             raise ValueError(f"Source {index} (github): 'max_issues' must be an integer")
 
+        # Validate enable_codebase_analysis if specified (C3.5)
+        if 'enable_codebase_analysis' in source and not isinstance(source['enable_codebase_analysis'], bool):
+            raise ValueError(f"Source {index} (github): 'enable_codebase_analysis' must be a boolean")
+
+        # Validate ai_mode if specified (C3.5)
+        if 'ai_mode' in source:
+            ai_mode = source['ai_mode']
+            if ai_mode not in self.VALID_AI_MODES:
+                raise ValueError(
+                    f"Source {index} (github): Invalid ai_mode '{ai_mode}'. "
+                    f"Must be one of {self.VALID_AI_MODES}"
+                )
+
     def _validate_pdf_source(self, source: Dict[str, Any], index: int):
         """Validate PDF source configuration."""
         if 'path' not in source: