feat: POST /auth/workspaces — create an additional collective from an existing account

Until now collectives only existed at registration; an account with a
personal workspace had no path to start one. The creator becomes Owner
and gets a session scoped to the new workspace.

pnpm-lock.yaml

@@ -145,6 +145,12 @@ importers:
 
   apps/media-worker:
     dependencies:
+      '@aws-sdk/client-s3':
+        specifier: ^3.1146.0
+        version: 3.1146.0
+      pg:
+        specifier: ^8.23.1
+        version: 8.23.1
       pino:
         specifier: ^9.3.2
         version: 9.14.0
@@ -152,6 +158,9 @@ importers:
       '@types/node':
         specifier: ^22.5.0
         version: 22.20.5
+      '@types/pg':
+        specifier: ^8.23.1
+        version: 8.23.1
       tsx:
         specifier: ^4.17.0
         version: 4.23.15