fix(macos): unify custom window frame with Win/Linux (bitsdojo)

[ZhuchkaTriplesix]

Problem

On macOS Querya shows dual chrome: native system titlebar + traffic lights, then a second Flutter QueryaWindowTitleBar. Windows/Linux use bitsdojo custom frame (BDW_CUSTOM_FRAME | BDW_HIDE_ON_STARTUP); macOS MainFlutterWindow still subclasses plain NSWindow.

Fix (in progress / PR)

• macos/Runner/MainFlutterWindow.swift: subclass BitsdojoWindow, enable custom frame + hide-on-startup (matches bitsdojo README)
• QueryaWindowTitleBar: leading inset 72px on macOS so menus/logo clear traffic lights; Win/Linux stay 16px

Follow-ups (optional)

• Hide in-bar File/Edit/Connection/Help on macOS (rely on system menu from MainMenu.xib) or wire system Preferences… (⌘,) to showPreferencesDialog
• Theme-sync native traffic-light appearance if needed on light themes
• Document macOS window setup in docs/architecture.md

Acceptance

• Single titlebar row on macOS (no stacked native + Flutter bars)
• Traffic lights visible; drag region works via MoveWindow
• Startup: no 800×600 flash before doWhenWindowReady sizing

[ZhuchkaTriplesix]

Fixed in #474 (merged to dev).