Embed distribution channel in CLI binary instead of relying on `aspire.config.json`

[radical]

Summary

The Aspire CLI should know its distribution channel — stable, daily, or pr — via build-time metadata embedded in the binary, rather than reading a mutable "channel" setting from aspire.config.json.

Proposed channels

Channel	Built from
stable	Release branches, official builds
daily	main, official daily builds
pr	PR CI builds, localhive

Mechanism

1. New MSBuild property — <CliChannel>stable</CliChannel> — set per build configuration:

   • Official release builds: stable
   • Official daily builds: daily
   • localhive / PR scripts: pr

2. Bake into binary — surface as [assembly: AssemblyMetadata("CliChannel", "stable")] so it can be read at runtime without sidecar files.

3. Runtime behavior — PackagingService.GetChannelsAsync() uses the embedded channel as its default instead of falling back to an implicit "whatever NuGet feeds are configured" channel. The embedded channel determines:

   • Which NuGet feeds to search for packages
   • Which CLI download base URL to use for aspire update --self
   • Whether self-update is available at all (PR builds: no)
   • Which package quality to search for (stable → stable only, daily → prerelease)

4. Remove "channel" from aspire.config.json — the --channel CLI argument on aspire update can remain as an override for power users, but the default comes from the embedded metadata.

Key files

File	Change
src/Aspire.Cli/Aspire.Cli.csproj	Add CliChannel property, emit assembly metadata
src/Aspire.Cli/Packaging/PackagingService.cs	Read embedded channel, use as default for GetChannelsAsync()
src/Aspire.Cli/Commands/UpdateCommand.cs	Use embedded channel as default for --self update
src/Aspire.Cli/Configuration/AspireConfigFile.cs	Remove Channel property
eng/Bundle.proj	Set CliChannel based on build type
localhive.sh / localhive.ps1	Set CliChannel=pr when building
eng/clipack/Common.projitems	Set CliChannel for archive builds

Related

• CLI packaging, distribution mode, and channel overhaul #15949 — Overall tracking issue for CLI packaging overhaul