fix: handle non-ok HTTP responses in connection store checkHealth

checkHealth previously ignored non-ok responses (e.g. 503), silently
doing nothing when the server reported unhealthy. Add else branch to
transition connected → disconnected on non-ok status. Add tests for
connected → disconnected on fetch failure and offline → reconnected
on health check success.

apps/web/src/stores/connection-store.ts

@@ -51,6 +51,10 @@ export const useConnectionStore = create<ConnectionState>((set, get) => ({
         } else {
           set({ lastHealthCheck: Date.now() });
         }
+      } else {
+        if (get().status === "connected") {
+          get().setDisconnected();
+        }
       }
     } catch {
       if (get().status === "connected") {

tests/unit/web/connection-store.test.ts

@@ -81,6 +81,24 @@ describe("connection-store", () => {
     expect(fetchMock).toHaveBeenCalledTimes(1);
   });
 
+  it("checkHealth transitions connected → disconnected on fetch failure", async () => {
+    fetchMock.mockImplementation(failHealth);
+    expect(useConnectionStore.getState().status).toBe("connected");
+    await useConnectionStore.getState().checkHealth();
+    expect(useConnectionStore.getState().status).toBe("disconnected");
+    expect(useConnectionStore.getState().failedSince).toBeTypeOf("number");
+  });
+
+  it("checkHealth transitions offline → reconnected on success", async () => {
+    fetchMock.mockImplementation(okHealth);
+    useConnectionStore.getState().setOffline();
+    expect(useConnectionStore.getState().status).toBe("offline");
+    await useConnectionStore.getState().checkHealth();
+    expect(useConnectionStore.getState().status).toBe("reconnected");
+    expect(useConnectionStore.getState().failedSince).toBeNull();
+    expect(useConnectionStore.getState().lastHealthCheck).toBeTypeOf("number");
+  });
+
   it("startPolling is idempotent", () => {
     useConnectionStore.getState().setDisconnected();
     useConnectionStore.getState().startPolling();