feat(console-web): synchronize Host state across tabs

- separate global Host state from tab-local shell and Page state
- replicate control-plane snapshots through a versioned BroadcastChannel
- handshake new tabs without publishing empty startup state
- reject self, stale, and malformed cross-tab messages
- suppress broadcast echoes while applying remote snapshots
- publish API snapshots and connection state atomically
- keep Page state private and update only mounted iframe documents
- test initial synchronization and protocol rejection paths

crates/wasmeld-console/web/src/sdk/protocol.ts

@@ -16,18 +16,27 @@ export type RuntimeAction = "start" | "stop" | "restart";
 export type ServiceAction = "start" | "stop" | "restart";
 export type PageLifecyclePhase = "activate" | "deactivate" | "dispose";
 
-export type HostSharedState = {
-  // This is a serializable snapshot, never a Solid signal crossing realms.
-  view: View;
+/**
+ * Control-plane state shared unconditionally between same-origin Host tabs.
+ *
+ * Navigation, search, dialogs, notifications and iframe caches are excluded:
+ * those values describe one browser tab rather than the Wasmeld runtime.
+ */
+export type HostGlobalState = {
   snapshot: BackendSnapshot | null;
   connection: ConnectionState;
-  query: string;
   apiBase: string;
   runtimeAction: RuntimeAction | null;
   serviceAction: string | null;
   deploymentAction: string | null;
 };
 
+export type HostSharedState = HostGlobalState & {
+  // This is a serializable snapshot, never a Solid signal crossing realms.
+  view: View;
+  query: string;
+};
+
 export type PageCommand =
   | { type: "refresh" }
   | { type: "navigate"; view: View }