feat(shell): add mini-pane window mode with hover-to-restore overlay

[130rockirt]

Summary

Add a title-bar mini-pane button that shrinks the desktop window to a 380x480 always-on-top pane. A draggable hover overlay offers a restore button that returns the window to its previous bounds and maximized state.

Changes

• Wire the mini command and state events through the shared desktop contract and preload bridge.
• Collapse secondary chrome while mini mode is active; add localized restore and drag controls.
• Unmaximize before restoring normal bounds, and preserve the original minimum size and always-on-top setting.
• Query the main process when mounting so renderer reloads recover the current mini state; newer toggle events take precedence over an older query response.
• Use weak window references and a dedicated mini-window stylesheet to satisfy the 700-line limit.
• Rebase onto develop after merging fix(composer): route dropped document uploads through the desktop bridge #1277 (08d8796fe).

Tests

• 21 focused tests passed for window transitions, renderer state recovery, title-bar controls, overlay markup, and desktop IPC handling.
• File-line gate passed.
• npm run typecheck, npm run build, and npm run lint passed.
• After the final rebase, all 42 combined attachment and mini-window regression tests passed.

[130rockirt]

Added a follow-up fix (a2946c8): exiting mini mode while the window is maximized kept the mini-sized normal frame, because setBounds() is a no-op on a maximized window. The restore path now unmaximizes before applying the saved bounds, so restoring puts the window back at the pre-mini size. Covered by a new unit test and verified end-to-end with Electron on a 1280x800 @150% display.

[XingYu-Zhong]

Reviewed the mini-window behavior and rebased it onto develop after #1277. Fixed renderer reload state recovery, query/event ordering, original minimum-size and always-on-top restoration, and the CSS line-limit failure. Corrected the unrelated PR description. Typecheck, build, lint, and all 42 combined attachment/mini-window regression tests pass; final shared renderer/preload/main typechecks also pass.