fix(chat-question-template): guard example-prompt fetch against unmount

[Aias00]

Related issue

Closes #2081

Summary

In chatQuestionTemplate, a mount-only useEffect called queryExamplePrompt, which awaits chatService.queryChatExamplePrompt({}) and then calls setExamplePromptList(res) with no mounted guard. If the component unmounted before the promise resolved, setState fired on an unmounted component. Added a mountedRef (useRef(true), set false in the mount effect's cleanup) and guard if (res && mountedRef.current) before setState, mirroring the NotificationNav pattern.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • npx tsc --noEmit -p chat2db-community-client/tsconfig.json — no errors for chatQuestionTemplate/index.tsx.
  • npx eslint src/pages/main/chat/chatQuestionTemplate/index.tsx — no errors.
• Manual verification: On unmount before the fetch resolves, mountedRef.current === false skips the setExamplePromptList call.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: N/A.
• Database or driver compatibility: N/A.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: N/A.
• Backward compatibility: Only skips setState after unmount; mounted behavior unchanged.

Reviewer map

• Start here: pages/main/chat/chatQuestionTemplate/index.tsx — mountedRef = useRef(true), mount useEffect sets it true and clears it in cleanup, and queryExamplePrompt guards if (res && mountedRef.current).
• Failure condition: setExamplePromptList still fires on an unmounted component during the on-mount fetch.
• Rollback or disable path: Revert this single commit.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: The fix, verification, and PR description were produced with Claude Code assistance.

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[openai0229]

Reviewed the latest frontend-only head. The unmount guard is scoped correctly, and the relevant frontend build/lint/test and JavaScript CodeQL checks pass.