Enable Multi-User Project Access

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Current State:
Projects are currently single-user only, limiting collaboration possibilities.

System Design:

• Accounts can have multiple users with roles
• Projects belong to accounts, not individual users
• Every user gets a personal "Account" by default

Requirements:

1. Project Access Control

• Allow account admins to add/remove users
• Define user roles (admin, member)

2. Related database schema/permission updates via Directus Sync

3. API Updates

• Account management endpoints
• User invitation system
• Role management
• Access validation

5. Email Notifications

• Account invitations
• Role changes
• Access updates

Access Levels:
Intentionally don't want to do "Account-Project" relations yet to keep it simple first

• Account Admin: Full control + user management
• Account Member: Can use projects
• Personal Account: Default for all users

Security Considerations:

• Validate all account access
• Protect personal accounts
• Audit logging for changes
• Clear permission boundaries

Migration:

1. Create personal accounts
2. Preserve existing projects
3. Enable multi-user gradually

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ECHO-71 Enable Multi-User Project Access