[Explorer] Desktop - Spawn Location Selection on Login

**Is your feature request related to a problem? Please describe.**
Currently, when a user launches the Explorer client and logs in successfully, they're dropped directly into the default spawn point (Genesis Plaza) with no option to choose where to land. This means users who want to go somewhere specific have to spawn in, then navigate or teleport elsewhere manually, adding friction right at the start of the session — especially for users who already know where they want to be.

**Describe the solution you'd like**
Add a "choose your destination" step to the login flow, similar to the experience on the mobile app. After a user successfully logs in but before being dropped into the world, show a UI that lets them pick a spawn location — for example: Genesis Plaza (default), a recently visited place, a saved/favorite place, or a search/jump-to-coordinates option. This would sit as an optional screen between login success and world load, with a clear "just take me to Genesis Plaza" default/skip option for users who don't want to choose each time.

**Describe alternatives you've considered**
There are a few different directions this could take, worth exploring further:
- Keeping a simplified version of current behavior, but improving in-world teleport/search so reaching a destination after spawning is faster.
- Auto-spawning at the user's last visited place instead of a full picker — lighter-weight, though it removes explicit choice.
- A settings-based persistent custom default spawn point, for users who always want to land in the same place.
- Some combination of the above, depending on how much control vs. simplicity we want to prioritize.

Happy to align with design/product on which direction fits best with the overall onboarding vision.

**Additional context**
This mirrors an existing pattern already used on the Decentraland mobile app, where users get a destination-selection UI after login. Bringing this to the desktop Explorer client would create consistency across platforms and reduce onboarding/session-start friction.

The payload names no files or tests; begin by tracing the desktop Explorer login flow and comparing it with the mobile app's destination-selection UI. Align on the destination options and default/skip behavior, then consider the work complete when an optional selection step appears after successful login and before world loading.

Written by the indexing model from the issue text.