fix: Cmd+W closing wrong window when Settings is open

[datlechin]

Summary

• Clear CommandActionsRegistry.shared.current in windowDidResignKey so stale main-window actions don't persist when a non-main window (Settings, Welcome) becomes key
• Simplify the Close Tab button action by removing a redundant main-window coordinator fallback that resolvedCloseTabActions already covers

Root cause

CommandActionsRegistry was only cleared on windowWillClose, not on windowDidResignKey. When the user opened Settings (Cmd+,) from a main editor window, the registry retained the main window's commandActions. Pressing Cmd+W then resolved those stale actions via resolvedCloseTabActions and called closeTab() on the main window instead of closing the Settings window.

Test plan

• Open a database connection, Cmd+, to open Settings, Cmd+W — only Settings should close
• Open Settings from the Welcome window, Cmd+W — only Settings should close
• Cmd+W on the Welcome window (no Settings) — Welcome should close normally
• Cmd+W on a main editor tab — tab should close as before
• Rapid Cmd+W spam with Settings open — no unexpected window closures