feat(ui): add identity management for tenants and users

* Implement tenant and user creation in IdentityPage
* Add API calls for managing tenants and users
* Introduce tenant-scoped API requests
* Update sidebar to include identity navigation
* Create BooleanStatusBadge component for key status

schema/plans.dbml

@@ -6,7 +6,7 @@ Table plans {
   status text [not null, default: 'draft']       // draft, active, blocked, completed, cancelled, superseded
   priority text [not null, default: 'medium']    // low, medium, high, critical
   project_id bigint [ref: > projects.id]
-  tenant_key text
+  tenant_id text [ref: > tenants.id]
   owner text
   due_date timestamptz
   completed_at timestamptz
@@ -19,7 +19,7 @@ Table plans {
 
   indexes {
     project_id
-    tenant_key
+    tenant_id
     status
     priority
     owner