fix(notification-nav): guard on-mount async queries against unmount

[Aias00]

Related issue

Closes #2071

Summary

NotificationNav fires three queries on mount (queryNotificationList, queryUnreadCount, queryPopNotification) that resolve into setState calls (setList, setHasUnread, setSPopOpen, setSPopData, setNoSPopOpen, setNoSPopData) with no mounted guard or AbortController. If the component unmounted before the awaits resolved, setState fired on an unmounted component. Added a mountedRef (useRef(true), set false in the mount effect's cleanup) and an early return before setState in each query function.

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 NotificationNav/index.tsx.
  • npx eslint src/components/NotificationNav/index.tsx — no errors.
• Manual verification: On unmount before the on-mount queries resolve, the mountedRef.current === false guard skips the setState calls. The mount effect sets mountedRef.current = true on (re)mount and false on cleanup (StrictMode-safe).
• 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: components/NotificationNav/index.tsx — mountedRef = useRef(true), the mount useEffect sets it true and clears it in cleanup, and each of queryUnreadCount/queryNotificationList/queryPopNotification early-returns when !mountedRef.current.
• Failure condition: setState still fires on an unmounted component during on-mount queries.
• 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 unmount guards around notification queries and side effects. No blocking findings; LGTM.