fix: revert ADR edits and enforce immutable accepted records

Restore docs/adr to main; add check_adrs.py CI gate so existing ADR-*.md
files cannot be modified — supersede with a new numbered ADR instead.

.github/workflows/release.yaml

@@ -30,9 +30,15 @@ jobs:
           git fetch --depth=50 origin "${{ gitea.ref }}"
           git checkout FETCH_HEAD
 
+      - name: Fetch base branch for ADR immutability
+        run: git fetch --depth=1 origin main
+
       - name: Install checker dependencies
         run: pip install --quiet pyyaml
 
+      - name: ADR immutability (no edits to accepted records)
+        run: python scripts/check_adrs.py --base origin/main
+
       - name: Documentation rules (links, glossary, readability)
         run: python scripts/check_docs.py