Implement SQLite persistence layer (TDD)

- Add SQLite and UUID dependencies (go-sqlite3, google/uuid)
- Create database connection with automatic migrations
- Implement UserRepository with full CRUD operations
- Implement HabitRepository with JSON serialization for arrays
- Implement HabitEntryRepository with date range queries
- Add comprehensive test coverage for all repositories
- Fix User entity to default timezone to UTC when empty
- All tests passing with TDD approach (Red-Green-Refactor)

internal/infrastructure/persistence/sqlite/database.go

@@ -0,0 +1,48 @@
+package sqlite
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+type Database struct {
+	conn *sql.DB
+}
+
+func NewDatabase(dbPath string) (*Database, error) {
+	dir := filepath.Dir(dbPath)
+	if dir != "." && dir != ":" {
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			return nil, fmt.Errorf("failed to create data directory: %w", err)
+		}
+	}
+
+	conn, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %w", err)
+	}
+
+	conn.SetMaxOpenConns(1)
+
+	if err := conn.Ping(); err != nil {
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	if err := RunMigrations(conn); err != nil {
+		return nil, fmt.Errorf("failed to run migrations: %w", err)
+	}
+
+	return &Database{conn: conn}, nil
+}
+
+func (db *Database) Close() error {
+	return db.conn.Close()
+}
+
+func (db *Database) Conn() *sql.DB {
+	return db.conn
+}