feat(core): support gemini model switch in ai (#13631)

<img width="757" height="447" alt="截屏2025-09-22 17 49 34"
src="https://github.com/user-attachments/assets/bab96f45-112e-4d74-bc38-54429d8a54ab"
/>


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- New Features
- Subscription-aware AI model picker in chat: browse models with version
and category, see active selection, switch models, and receive
notifications when choosing pro models without a subscription.
Selections persist across sessions.
- Central AI model service wired into chat UI for consistent model
selection and availability.

- Changes
- Streamlined AI model availability: reduced to a curated set for a more
focused experience.
  - Context menu buttons can display supplemental info next to labels.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/components/src/context-menu/button.ts

@@ -193,6 +193,7 @@ export const menuButtonItems = {
     (config: {
       name: string;
       label?: () => TemplateResult;
+      info?: TemplateResult;
       prefix?: TemplateResult;
       postfix?: TemplateResult;
       isSelected?: boolean;
@@ -211,7 +212,7 @@ export const menuButtonItems = {
           return html`
             ${config.prefix}
             <div class="affine-menu-action-text">
-              ${config.label?.() ?? config.name}
+              ${config.label?.() ?? config.name} ${config.info}
             </div>
             ${config.postfix ?? (config.isSelected ? DoneIcon() : undefined)}
           `;