fix: Use lowercase alphanumeric nanoid for Docker compose project names

Docker compose requires project names to be lowercase alphanumeric
with hyphens/underscores only. The default nanoid alphabet includes
uppercase and special characters, causing build failures.

apps/server/preview/manager.test.ts

@@ -67,7 +67,7 @@ vi.mock('node:fs/promises', () => ({
 }));
 
 vi.mock('nanoid', () => ({
-  nanoid: vi.fn(() => 'abc123test'),
+  customAlphabet: vi.fn(() => vi.fn(() => 'abc123test')),
 }));
 
 import { PreviewManager } from './manager.js';

apps/server/preview/manager.ts

@@ -8,7 +8,7 @@
 
 import { join } from 'node:path';
 import { mkdir, writeFile, rm } from 'node:fs/promises';
-import { nanoid } from 'nanoid';
+import { customAlphabet } from 'nanoid';
 import type { ProjectRepository } from '../db/repositories/project-repository.js';
 import type { PhaseRepository } from '../db/repositories/phase-repository.js';
 import type { InitiativeRepository } from '../db/repositories/initiative-repository.js';
@@ -116,7 +116,8 @@ export class PreviewManager {
     );
 
     // 4. Generate ID and prepare deploy dir
-    const id = nanoid(10);
+    const previewNanoid = customAlphabet('0123456789abcdefghijklmnopqrstuvwxyz', 10);
+    const id = previewNanoid();
     const projectName = `${COMPOSE_PROJECT_PREFIX}${id}`;
     const deployDir = join(this.workspaceRoot, PREVIEWS_DIR, id);
     await mkdir(deployDir, { recursive: true });