feat(provisioning): require password at DID ceremony
- POST /v1/dids now requires a password field; relay hashes with argon2id
and stores the PHC string in accounts.password_hash
- perform_did_ceremony Tauri command updated to accept password: String and
include it in the relay request body
- New PasswordScreen.svelte collects and confirms password during onboarding
(min 8 chars, confirm-match validation)
- Onboarding state machine extended: handle → password → loading → did_ceremony
- Integration test: password-provisioned account can authenticate via createSession