initialize all App fields after allocator.create

Same pattern as 3dea554e (mcp/Server.zig): allocator.create returns
undefined memory, and struct field defaults (shutdown: bool = false)
are not applied when fields are set individually. Use self.* = .{...}
to ensure all fields including defaults are initialized.

src/App.zig

@@ -47,10 +47,17 @@ pub fn init(allocator: Allocator, config: *const Config) !*App {
     const app = try allocator.create(App);
     errdefer allocator.destroy(app);
 
-    app.config = config;
+    app.* = .{
-    app.allocator = allocator;
+        .config = config,
-
+        .allocator = allocator,
-    app.robots = RobotStore.init(allocator);
+        .robots = RobotStore.init(allocator),
+        .http = undefined,
+        .platform = undefined,
+        .snapshot = undefined,
+        .app_dir_path = undefined,
+        .telemetry = undefined,
+        .arena_pool = undefined,
+    };
 
     app.http = try Http.init(allocator, &app.robots, config);
     errdefer app.http.deinit();