Add regression coverage for Copilot Centralization Optimizer task fetch fallback

[Copilot]

The Copilot Centralization Optimizer had a failure mode around agent task collection: if the task API fetch failed, downstream analysis could lose the expected dataset shape. This change adds regression coverage around the fallback path so the workflow keeps producing a valid empty dataset.

• Problem locked in

  • Adds workflow-level regression coverage for the task collection fallback in copilot-centralization-optimizer.
  • Protects the contract that downstream steps receive task-summaries.json, even when gh api fails.

• Source + compiled workflow coverage

  • Verifies the markdown workflow still contains the guarded task-fetch path.
  • Verifies the compiled .lock.yml still materializes the same fallback behavior.

• Behavioral regression test

  • Extracts the Collect agent task data shell snippet from workflow frontmatter.
  • Runs it with a failing gh stub and asserts the workflow still writes an empty JSON array for downstream consumption.

cmd := exec.CommandContext(ctx, "bash", "-c", script)
// fake `gh` exits non-zero
output, err := cmd.CombinedOutput()

taskSummariesJSON, _ := os.ReadFile(filepath.Join(dataDir, "task-summaries.json"))
// expected fallback artifact for downstream analysis
string(taskSummariesJSON) == "[]"