Align Windows UI with macOS preview 0.3

[puppyben1]

What changed

• Rebuilt the Windows welcome screen to follow the macOS preview/0.3.0 layout.
• Aligned the Windows workbench shell, activity rail, sidebar, title bar, status bar, empty editor state, and right plugin rail with the macOS structure.
• Rebuilt the settings dialog with the seven macOS categories: General, Editor, Keymap, Terminal, LSP, AI & Commit, and Updates.
• Preserved Windows native window controls and existing setting bindings where supported.
• Added Simplified Chinese and English localization for the aligned UI.

Why

The Windows UI had diverged from the macOS preview/0.3.0 visual hierarchy, control placement, and settings content. This brings Windows back to the macOS product baseline while retaining Windows-native chrome.

Validation

• TypeScript typecheck
• Lint on all changed frontend files
• git diff --check
• Windows React/Tauri boundary verification
• Full frontend production build
• Native Tauri development launch reached the Windows executable

Follow-up

Final pixel-level review should be completed against native Windows screenshots, especially for settings categories without supplied macOS screenshots.