Report cumulative Autoloop metric improvement

[Copilot]

✨ Enhancement

Autoloop only surfaced the current best metric, leaving PRs/issues/state files without the starting baseline or total progress. CI-measured pending-ci fitness values also lacked a documented path back into visible state.

• State schema

  • Adds Initial Metric to the Machine State table.
  • Defines it as the first accepted metric, set once and never overwritten.
  • Documents legacy backfill behavior when older state files lack a baseline.

• Visible progress reporting

  • Updates PR body guidance to show cumulative fitness:

    Fitness: {best_metric} (started at {initial_metric}, {absolute_delta} / {improvement_pct}% improvement)

  • Adds initial metric and total improvement to the program issue status comment.
  • Adds total improvement to per-iteration comments and iteration history.

• Pending CI fitness reconciliation

  • Documents pending-ci as a tracked state.
  • Requires the next iteration to read CI-measured fitness from prior runs before proposing new work.
  • Refreshes Initial Metric, Best Metric, PR body, and issue status after CI fitness is resolved.

• Regression coverage

  • Adds prose/schema tests for initial metric tracking, cumulative improvement visibility, and pending-CI reconciliation.