chore: batch RSR compliance + proof fixes

- Workflow fixes (hypatia-scan path, SHA-pinning, SPDX headers)
- SCM migration to A2ML format
- CODE_OF_CONDUCT.md, CONTRIBUTING.md
- Lean4/Coq proof completions where applicable
- forbid(unsafe_code) for safe Rust crates

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/hypatia-scan.yml

@@ -41,10 +41,9 @@ jobs:
         run: |
           if [ ! -f hypatia-v2 ]; then
             echo "Building hypatia-v2 scanner..."
-            cd scanner
             mix deps.get
             mix escript.build
-            mv hypatia ../hypatia-v2
+            mv hypatia hypatia-v2
           fi
 
       - name: Run Hypatia scan