Multi-account support: store and switch between multiple Steam accounts

[pqzmggg]

Summary

Allow GameNative to store credentials/sessions for more than one Steam account and switch between them without logging out and re-entering credentials each time.

Problem

GameNative currently supports a single logged-in Steam account. Users who own games across multiple accounts (e.g. a main account, a regional account, a family/shared account) have to fully log out and log back in — including re-entering the password and completing Steam Guard / 2FA — every time they want to launch a game from a different library. This is slow and error-prone on mobile, and it risks triggering Steam's rate limiting on repeated logins.

Proposed solution

• Add an account switcher in the UI (e.g. on the login screen or in Settings) listing all saved accounts with avatar + persona name.
• Persist each account's refresh token separately so switching does not require re-entering a password or 2FA code, matching desktop Steam's "remembered accounts" behavior.
• Keep per-account state isolated:
  • separate library/app lists
  • separate download and install state
  • Wine prefix / container mapping remains keyed appropriately so installed games are not clobbered across accounts
• Add an Add account action and a Remove account action (removing an account should revoke/delete its stored token).
• Optionally: remember the last-used account and auto-login to it on app start.

Additional context

• Desktop Steam and the official Steam Mobile App both support multiple remembered accounts, so this is behavior users already expect.
• Since GameNative already stores a session token for the single-account case, this is largely a matter of turning a single stored credential into a keyed collection plus UI to select from it.
• Storage size impact should be minimal (tokens only); the main design question is whether installed game files under steamapps/common/ are shared or namespaced per account. Shared would save a large amount of storage for accounts owning the same title, but licensing checks would need to run per account at launch.

Alternatives considered

• Logging out and back in manually — works today, but slow and hits 2FA/rate limits.
• Multiple app instances / work profile cloning — device-dependent, duplicates storage, and not viable for all users.