Opt-in username/password login — profiles become real accounts. This is the data
layer: a per-profile login password, kept SEPARATE from the quick-switch PIN
(different security purpose; a 4-digit PIN must not become the password guarding a
public instance).
- Additive migration: profiles.password_hash column (idempotent, metadata-flagged).
- set_profile_password / verify_profile_password / profile_has_password /
get_profile_by_name (the login username = profile name, unique + case-insensitive).
- Security default: a profile with NO password is NOT loginable (verify returns
False) — unlike the PIN where "no PIN = always valid". You can't authenticate to
an account with no credential.
Tests: migration adds the column; set/verify; no-password-never-loginable; clearing;
name lookup; and password is fully independent of the PIN. 6 tests pass. Next:
the login endpoint + require_login gate (increment 2).
