Use PR base branch (not main) for DE1-SoC synthesis metrics baseline

[Copilot]

Synthesis diff generation was always comparing against artifacts from main, even when a PR targeted a different branch (e.g. multicycle). This updates the workflow to resolve the baseline from the PR’s actual target branch.

• Workflow baseline branch selection

  • In .github/workflows/ci.yaml (de1-soc-synthesis-metrics-diff), replaced hardcoded baseline branch:
    • from branch: main
    • to branch: ${{ github.base_ref }}

• Baseline artifact naming/path alignment

  • Renamed baseline download semantics from main to base to match behavior:
    • step name/id updated (Download base branch Quartus reports, download-base)
    • artifact path changed from main-reports to base-reports

• Diff input updates

  • Updated all synthesis comparison inputs to read baseline files from base-reports/...:
    • fitter summary
    • fitter utilization-by-entity
    • timing summary

- name: Download base branch Quartus reports
  uses: dawidd6/action-download-artifact@v3
  with:
    workflow: ci.yaml
    branch: ${{ github.base_ref }}
    name: de1-soc-quartus-reports-${{ matrix.config }}
    path: base-reports

[github-actions]

🔧 DE1-SoC Synthesis Report Summary Diff

• RV32I

  1. Fitter Summary

     @@ -1,4 +1,4 @@
     -Fitter Status : Successful - Mon May 18 04:47:41 2026
     +Fitter Status : Successful - Sat May 23 02:41:02 2026
      Quartus Prime Version : 25.1std.0 Build 1129 10/21/2025 SC Lite Edition
      Revision Name : utoss-risc-v
      Top-level Entity Name : top

  2. Fitter by entity
     No changes detected

  3. Timing
     No changes detected

• RV32IB

  1. Fitter Summary

     @@ -1,4 +1,4 @@
     -Fitter Status : Successful - Mon May 18 04:47:42 2026
     +Fitter Status : Successful - Sat May 23 02:40:16 2026
      Quartus Prime Version : 25.1std.0 Build 1129 10/21/2025 SC Lite Edition
      Revision Name : utoss-risc-v
      Top-level Entity Name : top

  2. Fitter by entity
     No changes detected

  3. Timing
     No changes detected

---

Comparing synthesis results from main branch vs. this PR

[TheDeepestSpace]

@copilot can you also make the same PR for multicycle branch?