[Synkronus Portal] Show Formulus onboarding QR in portal after user creation (and admin password reset)

[najuna-brian]

Description

When an admin creates a new user (or force-resets their password), the portal should display a downloadable Formulus QR code containing the server URL, username, and plaintext password. This removes the need to run synk qr or formulus/scripts/generateQR.ts manually and lets the admin copy/send credentials to the user in one step.

The QR must only be shown at the moment the plaintext password is still known - it must not be stored or retrievable later.

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Problem

Today, onboarding a Formulus user requires:

1. Creating the user in the Synkronus Portal (synkronus-portal)
2. Separately generating a QR code via the CLI (synk qr) or the Formulus script (npm run generate_qr)

That extra CLI step is awkward for admins who already work in the portal. After user creation, the portal only shows a success toast and closes the modal, the plaintext password is discarded immediately:

The same applies to admin password reset (handleResetPassword): success message, form cleared, modal closed — no QR.

On the backend, passwords are hashed on create/reset and never returned again, which is correct for security:

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Proposed solution

After a successful Create User or Admin Reset Password action, show a one-time success screen/modal that includes:

• Username
• Password (plaintext, shown once — same security model as today, but surfaced briefly for handoff)
• QR code image encoding FRMLS settings for Formulus
• Download QR button (PNG)
• Clear copy explaining this is shown once and cannot be retrieved later

When to show the QR

Event	Show QR?
Admin creates a new user	Yes
Admin force-resets a user's password	Yes
User changes their own password	No
Viewing an existing user later	No

Security constraints (non-negotiable)

• QR contains the unencrypted password (required by Formulus scan flow).
• Because passwords are hashed server-side and never stored in plaintext, the QR can only be generated client-side while the plaintext password is still in memory from the form submission.
• The QR/password must not be persisted in localStorage, sessionStorage, the backend, or any user record.
• Closing/dismissing the modal should discard the credentials from React state.
• No API endpoint should ever return or regenerate a user's plaintext password.

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QR image generation

Include the CLI’s logo overlay (qr_logo.png) though functional QR is the priority.

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Acceptance criteria

• After creating a user, admin sees a one-time screen with username, password, and scannable QR.
• After admin password reset, admin sees the same one-time screen for that user.
• Admin can download the QR as a PNG.
• Dismissing the screen clears credentials from memory; revisiting the user list does not show the QR again.
• QR payload is valid FRMLS v1 and works when scanned in Formulus Settings → Scan QR code.
• Own-password change flow is unchanged (no QR shown).
• No backend storage or API for plaintext passwords.

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Test plan

1. Create a new user in the portal → confirm QR appears, scan with Formulus → app configures server URL + credentials and can log in.
2. Reset a user’s password as admin → confirm QR appears with the new password; old QR/password no longer works.
3. Close the success modal → reopen user management → confirm QR/password are not shown again.
4. Change own password as a non-admin → confirm no QR is shown.
5. Download PNG → confirm file scans correctly in Formulus.