test: real-GitHub validation across trunk models

[joshua-temple]

Goal

Validate orchestrate + promote on real GitHub (not just the local act-based harness) across every trunk model the generator supports. The local e2e suite proves generator output and runs workflows under act; this issue proves the framework end-to-end against the real GitHub Actions runtime, environment gates, and API surface.

Approach

Stand up example test repos under the stablekernel org, one per trunk model:

• no-env — environments: [], single trunk, release-only lifecycle
• 2-env — minimal promotion chain
• 3-env — intermediate cascade
• 4-env cascade — full dev → test → uat → prod promotion cascade

For each repo, validate the real-GitHub behavior of:

• Orchestrate on merge to trunk (change detection, build/deploy callback dispatch, state write-back)
• Promotion between environments (SHA-pinned promotion, breaking-change gate, state propagation)
• Hotfix / re-promote flows
• Failure handling and idempotency (re-running a dispatch is safe)
• Dry-run codepaths producing emulated outputs without skipping

Scope notes

• These repos double as living examples for adopters; keep their manifests clean and minimal.
• Each repo wires the published composite actions and pins a cli_version.
• Capture any divergence from the local act harness as follow-up issues.

Impact

This is the credibility gate: it proves the framework works on real GitHub for every supported topology, not just under local emulation.