Initial commit: RR3 Community Server with web admin panel

- ASP.NET Core 8 REST API server
- 12 API endpoints matching EA Synergy protocol
- SQLite database with Entity Framework Core
- Web admin panel with Bootstrap 5
- User, Catalog, Session, Purchase management
- Comprehensive documentation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/RR3CommunityServer.http

@@ -0,0 +1,6 @@
+@RR3CommunityServer_HostAddress = http://localhost:5143
+
+GET {{RR3CommunityServer_HostAddress}}/weatherforecast/
+Accept: application/json
+
+###