feat: Add seed command support to preview deployments

Run project-specific initialization commands (DB migrations, fixture
loading, etc.) automatically after containers are healthy, before the
preview is marked ready. Configured via per-service `seed` arrays in
.cw-preview.yml.

apps/server/preview/manager.ts

@@ -25,6 +25,7 @@ import {
   isDockerAvailable,
   composeUp,
   composeDown,
+  execInContainer,
   composePs,
   listPreviewProjects,
   getContainerLabels,
@@ -230,7 +231,10 @@ export class PreviewManager {
         );
       }
 
-      // 10. Success
+      // 10. Run seed commands
+      await this.runSeeds(projectName, config);
+
+      // 11. Success
       const url = `http://${id}.localhost:${gatewayPort}`;
       log.info({ id, url }, 'preview deployment ready');
 
@@ -477,6 +481,21 @@ export class PreviewManager {
     );
   }
 
+  /**
+   * Run seed commands for each service that has them configured.
+   * Executes after health checks pass, before the preview is marked ready.
+   */
+  private async runSeeds(projectName: string, config: PreviewConfig): Promise<void> {
+    for (const [serviceName, svc] of Object.entries(config.services)) {
+      if (!svc.seed?.length) continue;
+      log.info({ projectName, service: serviceName, count: svc.seed.length }, 'running seed commands');
+      for (const cmd of svc.seed) {
+        log.info({ service: serviceName, cmd }, 'executing seed');
+        await execInContainer(projectName, serviceName, cmd);
+      }
+    }
+  }
+
   /**
    * Build gateway routes from a preview config.
    */