dirty scan speed testing

libmarlin/src/db/migrations/0005_add_dirty_table.sql

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+PRAGMA foreign_keys = ON;
+PRAGMA journal_mode = WAL;
+
+-- Track which files need re-indexing
+CREATE TABLE IF NOT EXISTS file_changes (
+  file_id   INTEGER PRIMARY KEY REFERENCES files(id) ON DELETE CASCADE,
+  marked_at INTEGER NOT NULL             -- UNIX timestamp
+);