fix(windows): integrate window controls into the app header

[wesbillman]

Summary

Extend the integrated window controls to Windows, keeping minimize, maximize/restore, and close in the Buzz header rather than a separate native title bar.

• Add an undecorated Windows window configuration and share the existing controls between Linux and Windows, including during identity setup.
• Extend the main-local-webview capability to Windows; keep web and macOS outside the integrated-controls path.
• Expand component coverage for Windows platform detection, keyboard actions, retry after failure, and controls remaining available during identity restoration.

Relationship to the Linux PR

This branch builds on the Linux implementation in #631. Its diff against main currently includes that prerequisite. The Windows-specific change is commit 22958cb0326e9507b4120edbeed9517dc88f1e5e. Coordinate merge order with #631 and refresh this branch after the Linux change lands; these are not independent competing implementations.

Screenshots

Windows before/after captures are pending. The only images supplied in this branch were the inherited Linux screenshots, already attached to #631. Those are not Windows evidence and are not relabeled here. Both review-only image files have been removed from this PR's final source diff. Windows captures should be attached directly to this description, not committed.

Validation

Current head: 2bd67ca9ebcef2f51e2914868b3982873e720e53. The cleanup commit removes only the two inherited PNGs; application code remains unchanged from the supplied Windows branch.

• git diff --check passes against upstream aa10599d43077b92f43655fe035e1bc0ae5e6afb.
• Required local gates passed on macOS at the clean current head: TypeScript, 39 hook-selected related unit tests in 7 files, design-system types/guards, and workspace Clippy. This is not a full test-suite or native Windows run.
• No browser cases were added or removed. Component tests cover dispatch and accessible controls, not native window-manager behavior. Hosted CI and review remain pending; automatic CI is Linux-only, so it does not establish Windows acceptance.

Before marking ready

• Attach genuine Windows before/after screenshots.
• Complete review, hosted CI, and the repository's on-demand Windows native validation.
• Exercise Windows header dragging/double-click, minimize, maximize/restore, close, edge resizing, and snapping, including at minimum window size and during identity setup.
• Confirm Linux controls and macOS behavior remain unchanged.
• Human testing confirmation; reconcile with fix(desktop): integrate Linux and Windows window controls #631 before merge.

[wesbillman]

Superseded by #631. The complete Windows branch is preserved as a parent of combined head 3adace1, verified pushed to the existing linux-window-chrome PR branch. #631 includes the shared startup-control repair and retains the outstanding Windows screenshots, native validation and human acceptance checklist. No branch deletion or history rewrite.