feat(desktop): add goose://new-session deep link to open fresh chat

[DOsinga]

Summary

Add support for the goose://new-session deep link URL scheme so that opening this URL always creates a fresh chat window in the desktop app, rather than focusing the most recent session.

This enables desktop widgets, keyboard shortcuts (Alfred/Raycast), Apple Shortcuts, and other automation tools to launch new Goose sessions without going through a terminal.

Changes

Single file change in ui/desktop/src/main.ts — adds new-session hostname handling in the three existing protocol URL dispatch points:

1. second-instance handler (Windows/Linux) — creates a new chat window and returns early
2. handleProtocolUrl (shared handler) — creates a new chat window, clears pending deep link, returns
3. open-url event (macOS) — creates a new chat window and returns early

Each follows the same pattern already used for bot/recipe deep links.

Testing

• pnpm lint ✅
• tsc --noEmit ✅
• Manual: open goose://new-session on macOS should open a fresh chat window

Closes #6509

[alexhancock]

nit: i would add an optional initial message param, so a message could be written elsewhere and then kick off a session with it.

we used to have a separate little launcher window that let us do this. unsure if we still do.

[DOsinga]

nit: i would add an optional initial message param, so a message could be written elsewhere and then kick off a session with it.

we used to have a separate little launcher window that let us do this. unsure if we still do.

yeah, that would be great. but I think also a bit of a security risk. we have deeplinks for recipes that ask the user to inspect the recipe. I suppose we could not auto-submit?