feat(skills): Add code-visualizer skill for auto diagram generation

.claude/skills/code-visualizer/README.md

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+# Code Visualizer
+
+Auto-generates and maintains visual code flow diagrams from Python module analysis.
+
+## Quick Start
+
+Simply describe what you want:
+
+```
+Generate a code flow diagram for the auth module
+```
+
+```
+Check if my architecture diagrams are up to date
+```
+
+```
+Show what architecture changes this PR introduces
+```
+
+## Features
+
+### Auto-Generation
+
+Analyzes Python imports and generates mermaid diagrams:
+
+```mermaid
+flowchart TD
+    main[main.py] --> auth[auth/]
+    main --> api[api/]
+    auth --> models[models.py]
+```
+
+### Staleness Detection
+
+Warns when diagrams become out of sync with code:
+
+```
+STALE: README.md diagram (last updated: Jan 1, code changed: Jan 15)
+Missing: new_module.py, api/v2.py
+```
+
+### PR Impact Analysis
+
+Shows architecture changes in pull requests:
+
+- New modules added
+- Changed dependencies
+- Deleted relationships
+
+## How It Works
+
+1. **Analyze**: Parse Python files for imports and classes
+2. **Generate**: Create mermaid diagrams from relationships (delegates to mermaid-diagram-generator)
+3. **Monitor**: Compare timestamps to detect staleness
+4. **Report**: Provide freshness status and recommendations
+
+## Skill Architecture
+
+```
+code-visualizer
+├── Analyzes: Python AST for imports/classes
+├── Detects: Stale diagrams via timestamps
+└── Delegates to:
+    ├── mermaid-diagram-generator (syntax)
+    └── visualization-architect (complex diagrams)
+```
+
+## Limitations (Important)
+
+- **Staleness is timestamp-based**: 70-80% accuracy, false positives common
+- **Python-only**: No TypeScript/JS/Rust support
+- **Static analysis**: Dynamic imports not detected
+- **Import-centric**: Internal logic changes invisible
+
+See SKILL.md for complete limitations and accuracy expectations.
+
+## Philosophy Alignment
+
+| Principle               | How This Skill Follows It                                           |
+| ----------------------- | ------------------------------------------------------------------- |
+| **Ruthless Simplicity** | Timestamp-based staleness is "good enough" for 90% of cases         |
+| **Zero-BS**             | Real AST parsing, no mock data, honest about limitations            |
+| **Modular Design**      | Single brick, delegates diagram syntax to mermaid-diagram-generator |
+
+## Integration
+
+Works with:
+
+- `mermaid-diagram-generator` skill for diagram syntax
+- `visualization-architect` agent for complex diagrams
+- PR review workflow for impact analysis
+
+## Dependencies
+
+- **Required**: mermaid-diagram-generator skill
+- **Recommended**: Python 3.8+, Git for enhanced staleness detection