Add rate field to GetQuoteResponse

[PurpleTheBest]

Summary

• Adds a rate field to GetQuoteResponse (proto + C# DTO) carrying the dest/source conversion ratio as an invariant-culture decimal string, truncated to 6 decimals.
• Populated in QuoteService.GetQuoteAsync from the route's IRateProvider and mapped through SolverProtoMapper.ToGetQuoteResponse. Single-leg paths make Layerswap's multiplicative path aggregate reduce to the provider's rate directly.
• Intentionally not part of the signing payload — it's informational and derivable from the already-signed amount / receive-amount pair.

Files

• protos/solver.proto — string rate = 14; on GetQuoteResponse
• csharp/src/Shared.Models/Models/QuoteDto.cs — public decimal Rate { get; set; }
• csharp/src/Infrastructure/Quote/QuoteService.cs — Rate = swapRate.Truncate(6) on the QuoteWithSolverDto initializer
• csharp/src/Shared.Proto/SolverProtoMapper.cs — maps quote.Rate.ToString(InvariantCulture) into the gRPC response

Test plan

• dotnet build csharp/src/Shared.Proto/Proto.csproj succeeds (regenerates gRPC stubs with new field)
• dotnet build csharp/src/Infrastructure/Infrastructure.csproj succeeds
• dotnet test csharp/tests/Util.Tests/Util.Tests.csproj — existing QuoteServiceTests stay green
• Manual gateway call: GetQuote response includes a non-empty rate field and is consistent with receive_amount / amount after fee subtraction
• StationAPI aggregator passes the new field through unchanged to downstream clients

🤖 Generated with Claude Code