Implement local SQLite index database with repositories

- Add SQLite database connection management with proper error handling
- Implement schema for files, chunks, blobs, and snapshots tables
- Create repository pattern for each database table
- Add transaction support with proper rollback handling
- Integrate database module with fx dependency injection
- Make index path configurable via VAULTIK_INDEX_PATH env var
- Add fatal error handling for database integrity issues
- Update DESIGN.md to clarify file_chunks vs chunk_files distinction
- Remove FinalHash from BlobInfo (blobs are content-addressable)
- Add file metadata support (mtime, ctime, mode, uid, gid, symlinks)

internal/database/database.go

@@ -0,0 +1,114 @@
+package database
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+type DB struct {
+	conn *sql.DB
+}
+
+func New(ctx context.Context, path string) (*DB, error) {
+	conn, err := sql.Open("sqlite3", path+"?_journal_mode=WAL&_synchronous=NORMAL&_busy_timeout=5000")
+	if err != nil {
+		return nil, fmt.Errorf("opening database: %w", err)
+	}
+
+	if err := conn.PingContext(ctx); err != nil {
+		if closeErr := conn.Close(); closeErr != nil {
+			Fatal("failed to close database connection: %v", closeErr)
+		}
+		return nil, fmt.Errorf("pinging database: %w", err)
+	}
+
+	db := &DB{conn: conn}
+	if err := db.createSchema(ctx); err != nil {
+		if closeErr := conn.Close(); closeErr != nil {
+			Fatal("failed to close database connection: %v", closeErr)
+		}
+		return nil, fmt.Errorf("creating schema: %w", err)
+	}
+
+	return db, nil
+}
+
+func (db *DB) Close() error {
+	if err := db.conn.Close(); err != nil {
+		Fatal("failed to close database: %v", err)
+	}
+	return nil
+}
+
+func (db *DB) Conn() *sql.DB {
+	return db.conn
+}
+
+func (db *DB) BeginTx(ctx context.Context, opts *sql.TxOptions) (*sql.Tx, error) {
+	return db.conn.BeginTx(ctx, opts)
+}
+
+func (db *DB) createSchema(ctx context.Context) error {
+	schema := `
+	CREATE TABLE IF NOT EXISTS files (
+		path TEXT PRIMARY KEY,
+		mtime INTEGER NOT NULL,
+		ctime INTEGER NOT NULL,
+		size INTEGER NOT NULL,
+		mode INTEGER NOT NULL,
+		uid INTEGER NOT NULL,
+		gid INTEGER NOT NULL,
+		link_target TEXT
+	);
+
+	CREATE TABLE IF NOT EXISTS file_chunks (
+		path TEXT NOT NULL,
+		idx INTEGER NOT NULL,
+		chunk_hash TEXT NOT NULL,
+		PRIMARY KEY (path, idx)
+	);
+
+	CREATE TABLE IF NOT EXISTS chunks (
+		chunk_hash TEXT PRIMARY KEY,
+		sha256 TEXT NOT NULL,
+		size INTEGER NOT NULL
+	);
+
+	CREATE TABLE IF NOT EXISTS blobs (
+		blob_hash TEXT PRIMARY KEY,
+		created_ts INTEGER NOT NULL
+	);
+
+	CREATE TABLE IF NOT EXISTS blob_chunks (
+		blob_hash TEXT NOT NULL,
+		chunk_hash TEXT NOT NULL,
+		offset INTEGER NOT NULL,
+		length INTEGER NOT NULL,
+		PRIMARY KEY (blob_hash, chunk_hash)
+	);
+
+	CREATE TABLE IF NOT EXISTS chunk_files (
+		chunk_hash TEXT NOT NULL,
+		file_path TEXT NOT NULL,
+		file_offset INTEGER NOT NULL,
+		length INTEGER NOT NULL,
+		PRIMARY KEY (chunk_hash, file_path)
+	);
+
+	CREATE TABLE IF NOT EXISTS snapshots (
+		id TEXT PRIMARY KEY,
+		hostname TEXT NOT NULL,
+		vaultik_version TEXT NOT NULL,
+		created_ts INTEGER NOT NULL,
+		file_count INTEGER NOT NULL,
+		chunk_count INTEGER NOT NULL,
+		blob_count INTEGER NOT NULL
+	);
+	`
+
+	_, err := db.conn.ExecContext(ctx, schema)
+	return err
+}