Add Aspire daily regression workflow

[danegsta]

DCP regressions can show up only when Aspire runs a real AppHost against the DCP binary, especially around container networking and persistent resources. This adds a GitHub Actions regression gate that exercises that path against the latest Aspire daily build before DCP insertion.

The workflow builds DCP, installs the daily Aspire CLI, scaffolds a file-based AppHost from the daily channel, preserves the generated daily #:sdk directive, and appends a committed AppHost body that validates executable, session container, and persistent container resources. The AppHost reports startup and per-resource health markers, and the script fails unless every expected resource becomes healthy.

A disabled AzDO stage is updated to the same CLI-based shape, but remains unwired with condition: false pending pipeline-policy review. The local script is intended for CI and does not clean up container runtime resources it creates; GitHub-hosted runner cleanup handles that for the active workflow.

Validation:

• Ran test/aspire/run-regression.sh locally against bin/dcp with the daily Aspire CLI; all expected resources reached healthy.

[Copilot]

Pull request overview

This PR adds an end-to-end Aspire regression gate that runs a real Aspire AppHost (executable + session/persistent containers on a shared network) orchestrated by a locally built DCP binary against the latest Aspire daily CLI, to catch DCP integration regressions (process orchestration, container creation, container networking) before a DCP build is inserted into Aspire. A new GitHub Actions workflow drives this on hosted Linux runners, and a previously-inactive AzDO stage is reshaped to the same CLI-based approach but kept disabled pending pipeline-policy review.

Changes:

• New test/aspire/run-regression.sh harness that scaffolds an AppHost from the daily channel, preserves the scaffolded #:sdk pin, appends a committed AppHost body, runs it via DcpPublisher__CliPath, and waits for each resource to become healthy.
• New test/aspire/apphost-body.cs scenario exercising an executable, a session container, and persistent containers with intentional mixed-case names/aliases.
• New .github/workflows/aspire-regression.yml workflow, updated (still disabled) .azure/pipelines/aspire-test.yml stage, and CONTRIBUTING.md documentation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/aspire/run-regression.sh	New CI harness; scaffolds/runs the AppHost and validates resource health (minor --help output range issue).
test/aspire/apphost-body.cs	New committed AppHost body defining the regression scenario resources.
.github/workflows/aspire-regression.yml	New GitHub Actions workflow; triggers include an undocumented pull_request gate.
.azure/pipelines/aspire-test.yml	Reworks the disabled AzDO stage to the CLI-based flow; artifact name/path verified against common-build.yml.
CONTRIBUTING.md	Documents the new regression test; trigger list omits PR runs present in the workflow.

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