feat: add migration runner with genesisProbeTable param

Forward-only SQLite migration runner lifted from authd (src/db/migrate.ts,
PR #14 / merge ced21ab) and parameterized for cross-project use. The single
deliberate API change vs. authd's source: the previously-hardcoded
GENESIS_PROBE_TABLE = 'users' is now an ApplyOptions.genesisProbeTable?: string
option (default 'users').

src/index.ts

@@ -0,0 +1,12 @@
+export {
+  applyMigrations,
+  listMigrations,
+  readAppliedRows,
+  stampMigration,
+} from './migrate.js';
+export type {
+  ApplyOptions,
+  MigrationFile,
+  MigrationRow,
+  MigrationSummary,
+} from './migrate.js';