Account provisioning/deprovisioning documented

Undocumented account provisioning means departing employees retain access indefinitely and new joiners receive inconsistent permissions — two direct violations of NIST 800-53 rev5 AC-2 (Account Management), which requires formal procedures for account creation, modification, review, and termination. CMMC 2.0 AC.L1-3.1.1 makes this a baseline requirement for any contractor handling federal information. FedRAMP rev5 AC-2 adds an auditable trail requirement. Without documented deprovisioning steps, a disgruntled ex-employee's credentials may remain valid long after their last day, and an auditor will flag the absence of written procedures as a control gap regardless of what the code does.

Create docs/account-management.md covering all four lifecycle stages. Write steps specifically enough that an on-call engineer with no prior context can execute them without asking questions.

# Account Management

## Provisioning (new user)
1. Admin navigates to Settings > Users > Invite
2. Enters email and selects role (viewer / auditor / admin)
3. System sends time-limited invite link (24 h expiry)
4. User completes registration and sets a password meeting policy

## Role Assignment
- Roles follow least-privilege: default is viewer
- Elevation to auditor or admin requires written approval in the team ticket tracker
- Role changes logged automatically in audit_logs table

## Deprovisioning (user departure)
1. Admin deactivates account in Settings > Users > [User] > Deactivate
2. All active sessions invalidated immediately (Supabase: `auth.admin.deleteUser`)
3. API keys and personal tokens revoked
4. Access confirmed revoked within 1 business day of departure notice