Unpackaged desktop app shares the installed Dev taskbar identity

Description

The unpackaged Electron app and an installed Dev build both use ai.opencode.desktop.dev as their Windows AppUserModelID. This lets Windows associate the installed application with an unpackaged Electron shortcut or pin. If that development target later disappears, the taskbar can resolve the group through the stale target and display the generic document icon instead of the packaged application icon.

This was reproduced on a downstream Windows build that preserves the same packaged/unpackaged identity relationship as current upstream dev. The collision originates from the AppUserModelID setup introduced in #23368; that PR correctly added an explicit identity, but the unpackaged fallback currently reuses the installed Dev identity.

The unpackaged process should use a distinct AppUserModelID while retaining the existing Dev user-data directory.

Plugins

N/A

OpenCode version

dev at 04284921ac

Steps to reproduce

1. Build and install the Windows Dev desktop application.
2. Launch the unpackaged Electron desktop application.
3. Confirm that both processes use ai.opencode.desktop.dev as AppUserModelID.
4. Leave a shortcut or pin for the unpackaged Electron target, then remove or move that target.
5. Launch the installed Dev application and observe that Windows can show the stale or generic taskbar identity instead of the packaged icon.

Screenshot and/or share link

N/A

Operating System

Windows 11

Terminal

Windows Terminal