Add generate-share-package endpoint for residence sharing

- Add POST /api/residences/:id/generate-share-package/ endpoint
- Add SharePackageResponse DTO with share code and metadata
- Add GenerateSharePackage service method to create one-time share codes
- Update JoinWithCode to deactivate share code after successful use

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

bruno-collections/casera-api/environments/Dev.bru

@@ -1,5 +1,5 @@
 vars {
   base_url: https://casera.treytartt.com
   api_url: {{base_url}}/api
-  auth_token: your-auth-token-here
+  auth_token: 64eea3e59ecdf58a35a4fb45f4797413a3f96456
 }