fix(sql-editor): sync action state on content changes

[openai0229]

Related issue

Closes #2259

Summary

Synchronize SQL editor toolbar availability directly from Monaco model changes instead of waiting for the existing 300 ms debounced value callback.

The new onContentChange path is intentionally limited to lightweight UI state. SQL parsing, completion, parameter hints, and the existing external onChange behavior remain on the debounced path, preserving the editor's performance boundary while covering paste, deletion, undo, redo, and programmatic model updates.

Affected surfaces

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

Verification

• Commands and results:
  • yarn eslint src/components/SQLEditor/editor/MonacoEditor/index.tsx src/components/SQLEditor/editor/SQLEditor/index.tsx src/components/SQLEditor/editor/SQLEditorWithOperation/index.tsx --max-warnings=0 - passed
  • yarn lint - passed
  • yarn test:i18n - passed
  • yarn build:web:community --app_version=5.3.0 - passed, including all Community prebuild tests
  • git diff --check - passed
• Manual verification: The branch-specific Community frontend started on port 8890; /workspace and the frontend-proxied /api/system both returned HTTP 200. Interactive paste automation was unavailable in the current browser environment.
• UI evidence: N/A - no controllable browser instance was available; source timing, production build, and runtime smoke checks were verified.

Risk and compatibility

• Public API or stored data: N/A - no API or persistence changes.
• Database or driver compatibility: N/A - the behavior is database-independent.
• Network, privacy, or security: N/A - no network, clipboard access, or data handling changes.
• Community / Local / Pro boundary: Community frontend source only; the shared editor behavior remains compatible with existing surfaces.
• Backward compatibility: The existing debounced onChange callback is unchanged. The new optional callback only synchronizes lightweight content-presence state.

Reviewer map

• Start here: chat2db-community-client/src/components/SQLEditor/editor/MonacoEditor/index.tsx, inside onDidChangeModelContent.
• Failure condition: Content-dependent actions remain disabled after a non-empty model change, or SQL parsing/completion begins running synchronously on every edit.
• Rollback or disable path: Revert this commit to restore the previous debounced-only toolbar synchronization.

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: Substantial AI assistance was used for source tracing, implementation, and verification.