fix(core): ai history of new users is always loading, enable online search by default (#11741)

Close [AI-69](https://linear.app/affine-design/issue/AI-69).

packages/frontend/core/src/blocksuite/ai/chat-panel/chat-panel-messages.ts

@@ -235,7 +235,10 @@ export class ChatPanelMessages extends WithDisposable(ShadowlessElement) {
         @scroll=${() => this._debouncedOnScroll()}
       >
         ${filteredItems.length === 0
-          ? html`<div class="messages-placeholder">
+          ? html`<div
+              class="messages-placeholder"
+              data-testid="chat-panel-messages-placeholder"
+            >
               ${AffineIcon(
                 isLoading
                   ? 'var(--affine-icon-secondary)'

packages/frontend/core/src/blocksuite/ai/chat-panel/index.ts

@@ -400,7 +400,7 @@ export class ChatPanel extends SignalWatcher(
         .createSessionId=${this._createSessionId}
         .updateContext=${this.updateContext}
         .host=${this.host}
-        .isLoading=${this.isLoading || !this._isInitialized}
+        .isLoading=${this.isLoading}
         .previewSpecBuilder=${this.previewSpecBuilder}
       ></chat-panel-messages>
       <ai-chat-composer

packages/frontend/core/src/modules/ai-button/services/network-search.ts

@@ -3,6 +3,7 @@ import {
   type Signal,
 } from '@blocksuite/affine/shared/utils';
 import { LiveData, Service } from '@toeverything/infra';
+import { map } from 'rxjs';
 
 import type { FeatureFlagService } from '../../feature-flag';
 import type { GlobalStateService } from '../../storage';
@@ -17,12 +18,18 @@ export class AINetworkSearchService extends Service {
     super();
 
     const { signal: enabled, cleanup: enabledCleanup } =
-      createSignalFromObservable<boolean | undefined>(this._enabled$, false);
+      createSignalFromObservable<boolean | undefined>(
+        this._enabled$,
+        undefined
+      );
     this.enabled = enabled;
     this.disposables.push(enabledCleanup);
 
     const { signal: visible, cleanup: visibleCleanup } =
-      createSignalFromObservable<boolean | undefined>(this._visible$, false);
+      createSignalFromObservable<boolean | undefined>(
+        this._visible$,
+        undefined
+      );
     this.visible = visible;
     this.disposables.push(visibleCleanup);
   }
@@ -35,8 +42,10 @@ export class AINetworkSearchService extends Service {
     this.featureFlagService.flags.enable_ai_network_search.$;
 
   private readonly _enabled$ = LiveData.from(
-    this.globalStateService.globalState.watch<boolean>(AI_NETWORK_SEARCH_KEY),
-    false
+    this.globalStateService.globalState
+      .watch<boolean>(AI_NETWORK_SEARCH_KEY)
+      .pipe(map(v => (v === undefined ? true : v))),
+    undefined
   );
 
   setEnabled = (enabled: boolean) => {