[CoR] Workflow does not allow restarting the current stage without restarting the entire workflow

OS: Win11 x64
Build Version: 0.12.7-alpha.0
Regression: Not a regression

Repro Steps:

1. Start a Create with Copilot workflow
2. Progress through multiple stages (e.g. Project Scaffolding → Local Development → Deployment)
3. Reach a stage where the user wants to rerun or regenerate the current stage
4. Observe available workflow actions

Expect:
Provide a "Restart Current Stage" capability that allows users to rerun the current stage while preserving artifacts generated in previously completed stages

Customers may want to rerun the current stage to validate changes, regenerate artifacts, or recover from unexpected workflow behavior after reviewing generated code, test results, or deployment outputs.

Allowing users to restart the current stage would:

• Reduce iteration cost
• Preserve completed work from previous stages
• Improve workflow recovery and usability
• Avoid requiring users to recreate the entire project for stage-level reruns

Actual:
There is no option to restart the current stage. Users must either continue forward or restart the entire workflow from the beginning.

Start by locating the Create with Copilot workflow implementation and its available workflow actions. Trace how stages preserve artifacts and how the full-workflow restart is handled; done means users can restart only the current stage while retaining artifacts from completed stages.