Switch back to CGO SQLite driver

- Replace modernc.org/sqlite with github.com/mattn/go-sqlite3
- Update connection string for go-sqlite3 syntax
- Keep all performance optimizations and pragmas

The CGO driver may provide better performance for write-heavy
workloads compared to the pure Go implementation.

internal/database/database.go

@@ -12,7 +12,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
-	_ "modernc.org/sqlite" // Pure Go SQLite driver
+	_ "github.com/mattn/go-sqlite3" // CGO SQLite driver
 )
 
 //go:embed schema.sql
@@ -94,10 +94,10 @@ func NewWithConfig(config Config, logger *slog.Logger) (*Database, error) {
 		return nil, fmt.Errorf("failed to create database directory: %w", err)
 	}
 
-	// Add connection parameters for modernc.org/sqlite
+	// Add connection parameters for go-sqlite3
 	// Enable WAL mode and other performance optimizations
-	dsn := fmt.Sprintf("file:%s?_busy_timeout=5000&_journal_mode=WAL&_synchronous=NORMAL&_cache_size=-512000", config.Path)
-	db, err := sql.Open("sqlite", dsn)
+	dsn := fmt.Sprintf("file:%s?_busy_timeout=5000&_journal_mode=WAL&_synchronous=NORMAL&cache=shared", config.Path)
+	db, err := sql.Open("sqlite3", dsn)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open database: %w", err)
 	}
@@ -126,7 +126,7 @@ func (d *Database) Initialize() error {
 	pragmas := []string{
 		"PRAGMA journal_mode=WAL",        // Already set in connection string
 		"PRAGMA synchronous=NORMAL",      // Faster than FULL, still safe
-		"PRAGMA cache_size=-524288",      // 512MB cache
+		"PRAGMA cache_size=-524288",      // 512MB cache (negative = KB)
 		"PRAGMA temp_store=MEMORY",       // Use memory for temp tables
 		"PRAGMA mmap_size=268435456",     // 256MB memory-mapped I/O
 		"PRAGMA wal_autocheckpoint=1000", // Checkpoint every 1000 pages