Feature: Full controller support — testing, mapping, and documentation

## Summary

Add full controller support to the Decentraland Explorer, including button mapping, sensitivity settings, and documentation.

## Context

Controller support has been requested multiple times over the past 1–2 years, particularly as more games are being created in Decentraland. Currently, some controller functionality may exist in the Explorer but it has not been fully tested, mapped, or documented.

## Proposed Work

- Fully test existing controller input handling in the Explorer
- Define and implement a complete button mapping scheme for common controllers (e.g. Xbox, PlayStation, generic gamepad)
- Add controller-specific sensitivity settings (separate from mouse sensitivity, which is currently capped at 2)
- Document supported controllers and configuration options for users
- Consider UX for button assignment/remapping in the settings UI

## Notes

- Mouse sensitivity cap increase specifically for controller use was discussed but should be handled as a separate, controller-specific setting to avoid affecting all mouse users
- This is a backlog item — no ETA within the next 2–3 months

Requested by Stoyan Tsekov via Slack

Start by auditing the existing controller input handling in the Unity Explorer, then trace the settings UI where mouse sensitivity is configured. Define the supported controller mappings, controller-specific sensitivity behavior, and any remapping UX before implementation. Done means common controllers are tested, configurable, and documented for users.

Written by the indexing model from the issue text.