[MVP] Pricing tier enforcement

Enforce the Free and Pro plan limits on workspace entities — projects, employees, clients, and user accounts. When a Free workspace reaches its limit, further additions are blocked with a clear upgrade prompt rather than silently failing or allowing unlimited growth.

Why this matters

Without enforcement, the Free tier has no real ceiling — a workspace can add unlimited projects, employees, and users. This makes the pricing model non-functional and removes the incentive to upgrade. Enforcement is a prerequisite for launching paid plans.

How it works

The planned limits for the Free tier are:

| Entity | Free limit |

|---|---|

| Projects | 5 |

| Employees | 10 |

| Clients | 3 |

| Viewer accounts | 3 |

| Editor accounts | 1 (Superadmin only) |

Pro plan has no limits on any of these entities.

When a user tries to create an entity that would exceed their plan's limit, the creation is blocked and a dialog explains which limit was reached with an option to upgrade to Pro. Existing data is never deleted when a workspace is downgraded — limits apply only to new additions.