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/tests.zig

@@ -40,7 +40,10 @@ comptime {
     _ = @import("config/faults.zig");
     _ = @import("storage/config_schema.zig");
     _ = @import("storage/migrations.zig");
+    _ = @import("storage/querylog_migrations.zig");
     _ = @import("storage/querylog_schema.zig");
+    _ = @import("storage/querylog_versions.zig");
+    _ = @import("storage/querylog_fixtures.zig");
     _ = @import("storage/provenance.zig");
     _ = @import("storage/repositories/context.zig");
     _ = @import("storage/repositories/crud.zig");