Several user accounts: a user list, per-user nickname and picture, the game's user selector, a save per user #2292

What is missing

hle_account.c has one fixed user (k_uid), its nickname from DM_NICK, and ShowUserSelector returns that user without asking.
Two people on one device share one save, and a game that lists users or asks who is playing (3D World + Bowser's Fury lists all users) only ever sees one.

What you propose

Our fork's 31fdd96, adapted to main:

• DM_USERS names a tab-separated file, one user per line: Uid (32 hex digits), nickname, profile image path (a JPEG, may be empty), at most 8. Without it nothing changes.
• ListAllUsers, ListQualifiedUsers, GetUserCount, GetUserExistence, GetNickname and LoadProfileImage answer from that list.
• ShowUserSelector calls a new hook, int front_user_select(char out[33]), on the game thread, blocking as front_text_input does: 1 picked, 0 cancelled (the cancel result's value is not yet checked against an SDK), -1 no picker. A weak default returns -1, so front ends without a picker behave as today.
• MountSaveData with the preselected user's Uid mounts DM_SAVE as now; another user's Uid mounts that user's own folder, created on first mount.

Saves: the old form carries forward

No existing save moves or changes.
The preselected user stays k_uid unless a front end says otherwise, so every existing save still belongs to the user who opens by default.
Other users' saves go beside it, never in it.
Our fork uses DM_SAVE_ROOT/<uid>/saves/<title ID>/save, which suits our iOS front end; for nxnative something like <DM_SAVE>.users/<uid>/ beside save/ is probably clearer.
Since our change, main has gained the device save (<DM_SAVE>_device), cloud sync (DM_SAVE_SYNC, <DM_SAVE>-backups) and save transactions; each user's save would use the same clone-and-commit path.
The device save stays shared, as on the Switch.

Front ends

Front-ends: a new optional hook and an optional DM_USERS file; a front end that uses neither sees no change.

Scope and size

About 190 lines with tests (t_account; a t_fs case for another user's mount and commit), plus a picker per front end that wants one, plus the save-sync work above.

Alternatives considered

• One install or one save folder per person: works today, but the game cannot see or switch users.
• A user per controller (as 76545a5 maps controllers to players): games ask for users through the selector, not by controller.

Questions

1. Is multi-user wanted in nxnative, or should it stay a front-end concern?
2. Which layout for other users' saves?
3. Should cloud sync cover every user or only the preselected one?
4. The user list: DM_USERS, the saved choices, or both? Should it show in launcher.json?

Evidence we would bring

Host tests for the list, nickname, picture, selector and another user's mount and commit; an existing save opening unchanged after the update; and a game that lists users and one that shows the selector, played with two users on a Mac and an iPad.

Platforms: Mac, iPhone, iPad