core: return structured server info with stop method from workspace server

- Enables graceful server shutdown for workspace management
- Removes unsupported serverUrl getter that threw errors in plugin context

packages/opencode/src/control-plane/workspace-server/server.ts

@@ -60,6 +60,20 @@ export namespace WorkspaceServer {
       fetch: App().fetch,
     })
     server.listen(opts.port, opts.hostname)
-    return server
+    return {
+      hostname: opts.hostname,
+      port: opts.port,
+      stop() {
+        return new Promise<void>((resolve, reject) => {
+          server.close((err) => {
+            if (err) {
+              reject(err)
+              return
+            }
+            resolve()
+          })
+        })
+      },
+    }
   }
 }

packages/opencode/src/plugin/index.ts

@@ -34,10 +34,6 @@ export namespace Plugin {
       project: Instance.project,
       worktree: Instance.worktree,
       directory: Instance.directory,
-      get serverUrl(): URL {
-        throw new Error("Server URL is no longer supported in plugins")
-      },
-      $: () => {},
     }
 
     for (const plugin of INTERNAL_PLUGINS) {