feat(windows): add mac-style project tabs

[Mucheen]

Summary

• add a macOS-style project tab bar below the Windows title bar
• show every project opened in the current window and allow one-click project switching
• keep the existing title-bar project menu for project management actions

What changed

• added a small project-tab model that preserves project order and normalizes the active state to a single project
• added an accessible horizontal tab list using role=tablist, role=tab, and aria-selected
• highlighted the active project, disabled tabs while a project switch is in progress, and exposed the full project path as a tooltip
• mounted the tab bar directly below TitleBarWithSettings; it stays hidden when no project is open
• added focused model and component contract tests plus implementation notes

Verification

• bun test src/features/window/utils/project-tab-bar-model.test.ts src/features/window/components/project-tab-bar.test.ts
• related project-switching regression tests: 9 passed
• bun run typecheck
• targeted Vite Plus lint
• git diff --check
• .\scripts\build-windows.ps1 -Configuration Release
• WebView2 CDP check confirmed six project tabs render, clicking an inactive tab updates aria-selected, and the title-bar project label follows the active project

[Mucheen]

CI follow-up:

• The first macOS run failed in LinuxDoAnonymousWebSessionTests.inactiveSessionReleasesItsWebView because the scheduled WebKit release had not completed before the test deadline.
• The test and implementation are unchanged in preview/0.3.0; this was a parallel scheduling flake rather than a Windows project-tab regression.
• The branch was updated with the latest preview/0.3.0 merge commit 2236acd8.
• The synchronized rerun passed all macOS and Windows checks. Local validation also passed the Release build, Windows boundary check, Rust workspace tests, and Tauri host tests.