feat: improve db abstraction (#238)

docs/db.md

@@ -0,0 +1,74 @@
+# Database Configuration
+
+Kandev supports two database backends: **SQLite** (default) and **PostgreSQL**.
+
+## SQLite (default)
+
+SQLite requires no external services and works out of the box.
+
+### Environment variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `KANDEV_DATABASE_DRIVER` | `sqlite` | Database driver |
+| `KANDEV_DATABASE_PATH` | `./kandev.db` | Path to the SQLite database file |
+
+### Config file (`config.yaml`)
+
+```yaml
+database:
+  driver: sqlite
+  path: ./kandev.db
+```
+
+No additional setup is needed — the database file is created automatically on first run.
+
+## PostgreSQL
+
+### 1. Create the database
+
+```sql
+CREATE USER kandev WITH PASSWORD 'your-password';
+CREATE DATABASE kandev OWNER kandev;
+```
+
+### 2. Configure Kandev
+
+#### Environment variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `KANDEV_DATABASE_DRIVER` | `sqlite` | Set to `postgres` |
+| `KANDEV_DATABASE_HOST` | `localhost` | PostgreSQL host |
+| `KANDEV_DATABASE_PORT` | `5432` | PostgreSQL port |
+| `KANDEV_DATABASE_USER` | `kandev` | Database user |
+| `KANDEV_DATABASE_PASSWORD` | (empty) | Database password |
+| `KANDEV_DATABASE_DBNAME` | `kandev` | Database name |
+| `KANDEV_DATABASE_SSLMODE` | `disable` | SSL mode (`disable`, `require`, `verify-ca`, `verify-full`) |
+| `KANDEV_DATABASE_MAXCONNS` | `25` | Maximum open connections |
+| `KANDEV_DATABASE_MINCONNS` | `5` | Minimum idle connections |
+
+#### Config file (`config.yaml`)
+
+```yaml
+database:
+  driver: postgres
+  host: localhost
+  port: 5432
+  user: kandev
+  password: your-password
+  dbName: kandev
+  sslMode: disable
+  maxConns: 25
+  minConns: 5
+```
+
+### 3. Run
+
+```bash
+KANDEV_DATABASE_DRIVER=postgres \
+KANDEV_DATABASE_PASSWORD=your-password \
+kandev
+```
+
+Tables are created automatically on first run — no manual migrations needed.