Sloth-ninja lays the groundwork for firm administration

This is foundation work, not a visible new control panel yet. Sloth-ninja has added the underlying structure for a firm to manage members and, later, share access to AI providers while keeping existing individual setups working as before.

• Firm membership and roles, so the product can distinguish administrators from ordinary members.
• Firm policy settings, ready for later controls over member access but not active yet.
• Secure storage for firm-level provider credentials, paving the way for shared accounts.

The setup remains deliberately hands-on: an owner must apply the changes, create the firm, assign members and nominate an administrator. Importantly, a missing or failed firm setup will not prevent someone from signing in.