storage: version querylog.db and migrate it in place, never reset a healthy file

querylog.db carries a schema version; migrations run at startup as one transaction after a vacuumed 0600 backup, and every failure refuses startup (exit 2, no systemd restart loop) instead of starting empty. corruption is the only automatic recreate left. the cut gate now requires a fixture-proven migration or an explicit versioned break with restore instructions, and locks shipped migration files and fixtures byte-for-byte.

src/storage/repositories/queries_repo.zig

@@ -2518,7 +2518,10 @@ const recompute_checks = [_]struct { projection: []const u8, recompute: []const
     },
 };
 
-fn expectProjectionsMatchRecompute(database: *db.Db) !void {
+/// Exported for `querylog_migrations.zig`'s fixture and migration tests: the
+/// authority on projection coherence is this file, and a second copy of the
+/// recompute SQL there would be free to drift from the writer it checks.
+pub fn expectProjectionsMatchRecompute(database: *db.Db) !void {
     for (recompute_checks) |check| {
         var buf: [4096]u8 = undefined;
         const sql = try std.fmt.bufPrint(