Fix codegen for HTTP endpoints with Startup.Configure() pattern

[jeremydmiller]

Summary

Fixes #2363

• Root cause: When using the old ASP.NET Core Startup.Configure() hosting pattern, MapWolverineEndpoints() is called during host startup — not during Build(). The JasperFx codegen command only called Build(), so Configure() never ran and HTTP endpoints were never discovered.
• Fix: Upgrades JasperFx to 1.22.0 which adds a --start flag to the codegen command. Running dotnet run -- codegen write --start starts the host before code generation, ensuring Startup.Configure() executes and all HTTP endpoints are discovered.
• Sample project: Adds StartupStyleTarget in src/Http/ that uses the old Startup pattern and validates the fix — codegen write --start generates both GET_api_test.cs and POST_api_items.cs.

Usage for affected users

# Instead of:
dotnet run -- codegen write

# Use:
dotnet run -- codegen write --start

Test plan

• dotnet run -- codegen write on StartupStyleTarget produces no HTTP files (reproduces bug)
• dotnet run -- codegen write --start on StartupStyleTarget produces both GET_api_test.cs and POST_api_items.cs (fix works)
• Existing CodeGenTarget project (modern style) continues to work without --start

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