Add startup window state preference (#1367)

[SukuWc]

Closes #1367.

What

Adds a Startup window state radio in Preferences → General that controls how the window appears when Grid Editor launches:

Option	Behavior
Open in a normal window	Show normally (default)
Open minimized to the taskbar	minimize() — sits in the taskbar/dock
Open hidden in the tray	Stays hidden; tray icon on Windows/Linux, dock icon on macOS

This addresses the request to start the editor minimized/unobtrusively (useful when it auto-starts with the system). The "if already running, open the window" half was already handled by the single-instance lock and is hardened here.

How

• New persistent setting startupWindowState ("normal" | "taskbar" | "tray", default "normal") in app-helper.store.ts, persisted via the existing app-settings machinery.
• Preferences.svelte: a MeltRadio matching the adjacent "Run application in background" control.
• main.ts:
  • Window is created with show: false and shown on ready-to-show (also removes the white flash on normal launch); the chosen startup state is applied there.
  • second-instance handler now restores + shows + focuses the window on all platforms (previously show() was skipped on macOS, and only minimized windows were restored), so a minimized/tray start is always recoverable by relaunching. The deeplink parse is guarded so a plain relaunch no longer throws on new URL().

Testing

• npm run web-build passes.
• Verified on Linux: normal launch shows the window; relaunching a running instance triggers the single-instance handler without errors and re-focuses the existing window.
• ⚠️ Needs cross-platform confirmation: the taskbar (minimize) and tray (hide) paths could not be visually verified on the dev machine's tiling window manager (no tray/taskbar/minimize support there). Please confirm on Windows and macOS that those two options land the window minimized/hidden as intended and that it restores correctly.

🤖 Generated with Claude Code

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[Greg-Orca]

Mac OS ok

[narayb]

Tested on Windows 11:

• Minimized to taskbar works as expected.
• Minimized to tray doesn't work, the application doesn't appear on the tray at all, nor does it start normally. It potentially requires the keep app minimized after closeing the window setting on ON?

Tested on Fedora Workstation 44 (GNOME, Wayland):

• Minimized to taskbar doesn't work, because there is no taskbar, AFAIK no Wayland window is created. Because the app is running, but no window was created, there's no way to change the option back in the GUI, so the user has to fix this in the config.json.
• Minimized to tray also doesn't work for the same reasons, no tray exists on GNOME DE. Because of this no Wayland window is created and the GUI app stays inaccessible. Once again, has to be fixed in the config.json.