feat(init): apply base URL template to discovered apps

Discovered Docker apps now use the same buildAppUrl logic as
integrations when a base host is set, instead of using the raw
Docker socket URL (e.g. http://container:5432).

Extracts shared buildUrl helper and adds buildAppUrl that derives
a slug from the container name. Also passes publishedPort through
the DiscoveredApp type so host:port mode works correctly.

packages/api/src/router/onboard/onboard-router.ts

@@ -157,6 +157,7 @@ export const onboardRouter = createTRPCRouter({
         containerId: string;
         containerName: string;
         suggestedUrl: string;
+        publishedPort: number | null;
         iconUrl: string | null;
       }[],
     };
@@ -228,6 +229,7 @@ export const onboardRouter = createTRPCRouter({
             containerId: container.Id,
             containerName,
             suggestedUrl,
+            publishedPort,
             iconUrl,
           });
         }