Defer server file changes until guarded restart activation

Persist beta, promotion, drift, and rollback payloads until occupancy and restart-capacity checks pass. Preserve rollback snapshots and campaign ordering, and allow held rollback campaigns to resume safely.

Fixes #28

Validation: 805 tests passed, Svelte checks clean, production build passed.

tests/unit/create-server.test.ts

@@ -645,7 +645,11 @@ describe('server creation map selection', () => {
         expect(await scanServerDrift(serverName)).toEqual([]);
         const mapPath = join(fixture.t5, serverName, 'configs', 'electric_cherry_map.cfg');
         await rm(mapPath);
-        expect((await runDriftDeployment({ servers: [serverName] })).totalRestored).toBe(1);
+        const repair = await runDriftDeployment({ servers: [serverName] });
+        expect(repair.totalRestored).toBe(1);
+        expect(existsSync(mapPath)).toBe(false);
+        const { activateFiles } = await import('../helpers/staged-files.js');
+        await activateFiles('campaign', repair.deploymentId!);
         expect(await readFile(mapPath, 'utf8')).toContain('set sv_maprotation "map zombie_cosmodrome"');
         expect(await scanServerDrift(serverName)).toEqual([]);
     });