ADR-0017: Weir's Backend Moves to C# on .NET 10

Status: Accepted

The server is C# on .NET 10, in apps/server. The web app stays React, TypeScript and Vite. The port kept the HTTP API and the SQLite schema unchanged, proven by the contract suite, and the switch in #523 removed the Python backend. Since then the numbered SQL migrations in the .NET server are the only source of schema changes, and configuration is loaded by WeirOptionsLoader into WeirOptions (replacing ADR-0008).

Full ADR source: docs/adr/ADR-0017-backend-on-dotnet.md