feat: add database skills for ClickHouse, PostgreSQL, and SQLite

- Add ClickHouse patterns skill
- Add PostgreSQL patterns skill
- Add SQLite patterns skill
- Update backend-developer agent to reference PostgreSQL and SQLite skills
- Update go-developer agent to reference ClickHouse, PostgreSQL, and SQLite skills
- Update capability-index.yaml with database integration capabilities

.kilo/agents/backend-developer.md

@@ -268,6 +268,8 @@ This agent uses the following skills for comprehensive Node.js development:
 | Skill | Purpose |
 |-------|---------|
 | `nodejs-db-patterns` | SQLite, PostgreSQL, MongoDB patterns |
+| `postgresql-patterns` | Advanced PostgreSQL features and optimization |
+| `sqlite-patterns` | SQLite-specific patterns and best practices |
 
 ### Package Management
 | Skill | Purpose |