refactor(community): refine workspace and desktop navigation

[openai0229]

Related issue

Closes #2708

Summary

This PR reorganizes the Community workspace and desktop chrome into compact, consistent navigation surfaces. It standardizes Lucide icon sizing, search controls, toolbar alignment, active states, workspace panel persistence, and title-bar shortcuts.

Windows receives a native-style application menu, stable draggable regions, visible window controls, and corrected maximize-state handling. macOS fullscreen state is synchronized with the frontend. Task-center behavior is intentionally excluded and is provided by a stacked PR.

Affected surfaces

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

Verification

• Commands and results:
  • yarn build:web:community: passed, including the Community frontend test suite, production Webpack build, and bundle verification.
  • mvn -pl chat2db-community-jcef -am -Dmaven.test.skip=false test: passed; tools ran 67 tests and JCEF ran 57 tests with no failures.
  • git diff --check origin/main...HEAD: passed.
• Manual verification: the Community title bar, sidebars, search interactions, Windows window controls, and macOS layout were iteratively exercised in the packaged desktop runtime before this split.
• UI evidence: see the screenshots and review history in the superseded PR refactor(task): rebuild Community async task system #2659.

Risk and compatibility

• Public API or stored data: no API or stored-data changes.
• Database or driver compatibility: no database or driver behavior changes.
• Network, privacy, or security: no network or credential-handling changes.
• Community / Local / Pro boundary: changes are Community-specific; shared frontend components keep existing behavior.
• Backward compatibility: workspace panel persistence accepts existing state and supplies defaults for the new layout.

Reviewer map

• Start here: CommunityMainPage, AppTitleBar, CommunityMainActionBar, WorkspaceLeftActionBar, WorkspaceExtendNav, and WindowsCommunityWindowChrome.
• Failure condition: controls overlap, window buttons become unreachable, draggable title-bar regions intercept actions, or persisted workspace panels open incorrectly.
• Rollback or disable path: revert this PR; no storage migration or backend API rollback is required.

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 implementation, platform debugging, tests, and review. The contributor manually reviewed and tested the resulting behavior.