Expand skills library: Integrate 6 skills across all agents with decision frameworks

[Copilot]

Skills library expanded from isolated usage to comprehensive cross-agent integration. Each agent now has 4-6 skills (was 1-2) organized by primary/secondary hierarchy with decision frameworks.

Changes

Skill Integration

• game-developer: Added testing-strategy, documentation-standards (testing 3D components, documenting mechanics)
• frontend-specialist: Added testing-strategy, security-by-design (component testing, input validation)
• test-engineer: Added react-threejs-game, performance-optimization, documentation-standards (3D testing, perf metrics, test docs)
• security-specialist: Added documentation-standards, testing-strategy (security docs, security testing)
• documentation-writer: Added isms-compliance, security-by-design, testing-strategy (ISMS refs, security docs, test examples)
• product-task-agent: Comprehensive all-skills integration matrix (6 skills with when/what/create guidance)

Documentation Structure

• Agent-skill integration matrices in both READMEs (bidirectional lookup)
• Decision frameworks: IF/THEN patterns for skill application
• Primary/secondary skill distinction with clear usage guidance
• 26 skill references across 6 agents (was ~8)

Pattern Example

### Primary Skills
| Skill | Pattern | Application |
| react-threejs-game | Canvas Setup | Use Canvas with proper camera, lighting, controls |
| performance-optimization | 60 FPS Target | Maintain 60fps using refs for mutations |

### Secondary Skills  
| Skill | Application |
| testing-strategy | Unit test game logic, mock Three.js rendering |

**Decision Framework:**
- IF creating 3D objects → Apply `react-threejs-game`: Use declarative JSX
- IF performance issues → Apply `performance-optimization`: Use instanced meshes

Impact

• Universal capabilities: testing-strategy and documentation-standards adopted by all agents (100%)
• Cross-functional work: Agents operate beyond primary domain (game-developer can test and document)
• Consistent patterns: 26 skill references ensure uniform approach

Validation

✅ YAML frontmatter (name, description, MIT license)
✅ Skills Integration sections with decision frameworks
✅ Skill path references (.github/skills/skill-name/SKILL.md)
✅ Integration matrices accurate
✅ Hack23 Agent Curator standards compliance

Original prompt

Expand the skills library .github/skills for all agents in .github/skills based on purpose of agents and project documentation.

Update skill/agent documentation in repo (see where current agents and skills are included)

Custom agent used: hack23-agent-curator
Org-level curator for Hack23 Copilot agents, enforcing GitHub config, MCP standards, and documentation quality

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