2 new efficiency skills to reduce cost and wasted cpu cycles in github actions and codespaces (#1766)

* fresh pull of updated stage with 2 skills and updated README only

* adjusted skills after feedback and used skill analyser to review

---------

Co-authored-by: Mark Heynes <mutl3y@heynes.biz>

skills/github-actions-efficiency/references/reporting.md

@@ -0,0 +1,42 @@
+# Efficiency Reporting and Follow-Up Review
+
+Load this reference when the user asks what changed, wants a before/after report, or asks for another pass over remaining expensive jobs.
+
+## Reporting Rules
+
+- Separate expected savings from measured savings.
+- Do not claim exact time or cost savings without before/after run data.
+- Call out confounders such as cache warm-up, changed matrix breadth, runner changes, or unusually small PRs.
+
+Use this phrasing when data is incomplete:
+
+`I can report the efficiency mechanisms that changed, but I cannot honestly claim exact minutes saved without comparing before/after GitHub Actions runs.`
+
+## What To Measure
+
+Gather:
+
+1. A baseline sample before the change
+2. A post-change sample after caches warm
+3. Per-workflow or per-job duration comparisons
+4. Avoided runs, skipped jobs, or avoided matrix legs
+
+Always separate:
+
+- PR wall-clock time
+- Total runner time across jobs
+- Work avoided entirely
+
+These answer different questions. A change can reduce runner spend without materially improving the fastest feedback path.
+
+## Follow-Up Review Pass
+
+After the first round of fixes is validated, inspect the remaining expensive jobs:
+
+- Compare setup time versus execution time
+- Identify heavyweight wrapper actions and confirm what they really enforce
+- Review whether each matrix dimension still serves an active decision
+- Recheck after caches warm
+- Break down the dominant slow step before proposing further changes
+
+Keep the follow-up compact. Report the next few highest-value opportunities, not a long wishlist.