Reorganize: Move all skills to skills/ folder

- Created skills/ directory
- Moved 272 skills to skills/ subfolder
- Kept agents/ at root level
- Kept installation scripts and docs at root level

Repository structure:
- skills/           - All 272 skills from skills.sh
- agents/           - Agent definitions
- *.sh, *.ps1       - Installation scripts
- README.md, etc.   - Documentation

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

skills/database-design/skill.md

@@ -0,0 +1,52 @@
+---
+name: database-design
+description: Database design principles and decision-making. Schema design, indexing strategy, ORM selection, serverless databases.
+allowed-tools: Read, Write, Edit, Glob, Grep
+---
+
+# Database Design
+
+> **Learn to THINK, not copy SQL patterns.**
+
+## 🎯 Selective Reading Rule
+
+**Read ONLY files relevant to the request!** Check the content map, find what you need.
+
+| File | Description | When to Read |
+|------|-------------|--------------|
+| `database-selection.md` | PostgreSQL vs Neon vs Turso vs SQLite | Choosing database |
+| `orm-selection.md` | Drizzle vs Prisma vs Kysely | Choosing ORM |
+| `schema-design.md` | Normalization, PKs, relationships | Designing schema |
+| `indexing.md` | Index types, composite indexes | Performance tuning |
+| `optimization.md` | N+1, EXPLAIN ANALYZE | Query optimization |
+| `migrations.md` | Safe migrations, serverless DBs | Schema changes |
+
+---
+
+## ⚠️ Core Principle
+
+- ASK user for database preferences when unclear
+- Choose database/ORM based on CONTEXT
+- Don't default to PostgreSQL for everything
+
+---
+
+## Decision Checklist
+
+Before designing schema:
+
+- [ ] Asked user about database preference?
+- [ ] Chosen database for THIS context?
+- [ ] Considered deployment environment?
+- [ ] Planned index strategy?
+- [ ] Defined relationship types?
+
+---
+
+## Anti-Patterns
+
+❌ Default to PostgreSQL for simple apps (SQLite may suffice)
+❌ Skip indexing
+❌ Use SELECT * in production
+❌ Store JSON when structured data is better
+❌ Ignore N+1 queries