Add sql skill

.claude/skills/sql/SKILL.md

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+---
+name: sql
+description: Help write, debug, and explore SQLite database queries using Kysely. Use when writing repository code, exploring data, debugging query issues, or understanding the database schema.
+---
+
+# SQL Database Helper
+
+## Databases
+
+| File | Purpose | When to use |
+|------|---------|-------------|
+| `db.sqlite3` | Development database | Writing/testing new features, running the dev server |
+| `db-prod.sqlite3` | Copy of production database | Exploring real data, investigating bugs, verifying assumptions about data shape |
+| `db-test.sqlite3` | Unit test database (blank + migrations) | Unit tests only |
+
+`db-prod.sqlite3` can be modified if the task requires it. **Never modify `db-copy.sqlite3`** — it is the untouched backup.
+
+## Schema
+
+All table definitions live in `app/db/tables.ts`. Read this file first to understand available tables, columns, and their types. Key conventions:
+
+- Every table has a numeric `id` primary key (type `number`)
+- Booleans are stored as `0`/`1` (type `DBBoolean`)
+
+## Exploring data
+
+When the user needs to explore or query existing data, use `sqlite3` CLI commands against the appropriate database.
+
+**Important:** Always quote table and column names with double quotes (`"TableName"`, `"columnName"`) because the schema uses camelCase naming and some names are reserved SQL keywords.
+
+```bash
+# Explore production data
+sqlite3 db-prod.sqlite3 'SELECT * FROM "User" LIMIT 5;'
+
+# Check schema of a table
+sqlite3 db-prod.sqlite3 '.schema "User"'
+
+# Count rows
+sqlite3 db-prod.sqlite3 'SELECT COUNT(*) FROM "User";'
+
+# Development database
+sqlite3 db.sqlite3 'SELECT * FROM "User" LIMIT 5;'
+```