Publish immutable short firmware download links

Mirror pinned GitHub release bytes at shorter version-specific Pages URLs. Verify size, SHA-256 and firmware format before publishing, and preserve deployed alias identities across later site builds.

Add RAK4631 Full Companion 1.17.1.10 preview2 UF2 and native DFU ZIP aliases, a short-download directory, documentation and CI regressions. Existing flashing tools use the ZIP URL without losing board-family checks.

Validation: 16 short-link and Pages guard regressions, hosted-doc routing tests, firmware picker tests, full MkDocs build and exact UF2/ZIP byte checks.

.github/workflows/run-unit-tests.yml

@@ -191,6 +191,11 @@ jobs:
       - name: Verify build output cleanup safety
         run: python3 -B test/test_build_output_safety.py -v
 
+      - name: Verify immutable short firmware downloads and Pages publishing
+        run: |
+          python3 -B test/test_firmware_shortlinks.py -v
+          python3 -B test/test_docs_firmware_shortlinks.py -v
+
       - name: Verify serial mOTA response deadlines and RX fairness
         run: |
           python3 -B test/test_mota_serial_deadline.py -v