feat: add browserdata/datautil helpers (#513)

* feat: add browserdata/datautil helpers (QuerySQLite, QueryRows, DecryptChromiumValue)

Phase 2 of architecture refactoring (RFC-002 Section 3):

- datautil/sqlite.go: QuerySQLite() — shared SQLite open/query/scan helper
  with optional journal_mode=off for Firefox databases
- datautil/query.go: QueryRows[T]() — generic helper (Go 1.20) that wraps
  QuerySQLite and collects results into a typed slice
- datautil/decrypt.go: DecryptChromiumValue() — unified Chromium decryption
  (DPAPI first, then AES-GCM/CBC fallback)
- datautil/sqlite_test.go: tests for all helpers

* refactor: move DecryptChromiumValue from datautil to browser/chromium

- Remove browserdata/datautil/decrypt.go (Chromium-specific, not a generic util)
- Will be added as browser/chromium/decrypt.go (unexported decryptValue)
  in the chromium extract methods PR
- Update RFCs to reflect the change
- Remove decrypt test from datautil tests

* refactor: move datautil to utils/sqliteutil for consistency

- Rename browserdata/datautil/ → utils/sqliteutil/
- Aligns with existing utils/ convention (fileutil, typeutil, byteutil)
- QuerySQLite/QueryRows are generic SQLite helpers, not browserdata-specific
- Update package name from datautil to sqliteutil
- Update both RFCs to reflect new location

* fix: apply review suggestions for sqliteutil

- QuerySQLite: validate dbPath exists before sql.Open to prevent
  silently creating empty databases
- Tests: check db.Close() errors with require.NoError

utils/sqliteutil/sqlite.go

@@ -0,0 +1,51 @@
+package sqliteutil
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+
+	// sqlite3 driver for database/sql
+	_ "modernc.org/sqlite"
+
+	"github.com/moond4rk/hackbrowserdata/log"
+)
+
+// QuerySQLite opens a SQLite database, optionally disables journal mode (required
+// for Firefox databases), runs the query, and calls scanFn for each row.
+//
+// It validates the database file exists before opening to prevent sql.Open from
+// silently creating an empty database.
+//
+// scanFn should return nil to continue iteration, or an error to skip the current
+// row (the error is logged at debug level and iteration continues).
+func QuerySQLite(dbPath string, journalOff bool, query string, scanFn func(*sql.Rows) error) error {
+	if _, err := os.Stat(dbPath); err != nil {
+		return fmt.Errorf("database file: %w", err)
+	}
+	db, err := sql.Open("sqlite", dbPath)
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+
+	if journalOff {
+		if _, err := db.Exec("PRAGMA journal_mode=off"); err != nil {
+			return err
+		}
+	}
+
+	rows, err := db.Query(query)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		if err := scanFn(rows); err != nil {
+			log.Debugf("scan row error: %v", err)
+			continue
+		}
+	}
+	return rows.Err()
+}