fix(xterm): dispose Terminal on unmount

[Aias00]

Related issue

Closes #2059

Summary

The Xterm mount useEffect called initXterm() which creates a new Terminal(), loads a FitAddon, registers xterm.onData(...), and calls xterm.open(...). The cleanup only removed the window resize listener — it never called xterm.dispose(), so every mount/unmount leaked a full Terminal instance (DOM, renderer, buffers, internal timers), plus the onData disposable and the FitAddon. Added xtermRef.current?.dispose() to the cleanup (dispose() also disposes loaded addons and event listeners), and reset the refs.

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 Xterm/index.tsx.
  • npx eslint src/components/Xterm/index.tsx — no errors.
• Manual verification: On unmount, xterm.dispose() is now called, tearing down the Terminal, the loaded FitAddon, and the onData listener.
• 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 adds cleanup on unmount; mount/render behavior unchanged.

Reviewer map

• Start here: components/Xterm/index.tsx — the useEffect([], ) cleanup now calls xtermRef.current?.dispose() and resets xtermRef/fitAddonRef to null.
• Failure condition: Terminal instances still leak across mount/unmount.
• 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.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[openai0229]

Reviewed the terminal disposal cleanup on unmount. LGTM.