feat(libSceNpManager): look up a user by account id while signed out

[evDev69]

What

Implements sceNpGetUserIdByAccountId(accountId, userId*). Account id 0 or a null output returns INVALID_ARGUMENT; any other account returns SIGNED_OUT with the output untouched, as sceNpGetAccountIdA already does.

Only shadPS4 (PS4) declares the signature, so it is recorded under "Unknown function info" in TechnicalDebt.

Tested

See shared notes. guest_np_manager checks the signed-out result, the untouched output, and both invalid-argument cases.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• AI-assisted: yes

[oneandonlydean]

Same as #1536: no title is shown reaching sceNpGetUserIdByAccountId on main.