Add EBNF-to-GBNF converter for llama.cpp constrained generation

Automated converter transforms RIDDL's EBNF grammar (258 rules)
into GBNF format for llama.cpp constrained text generation.
Features auto-classification of terminal vs structural rules
for whitespace insertion, hand-maintained overrides for 3
negative-lookahead patterns, and CI freshness check.

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

Author: reid-spencer

.github/workflows/scala.yml

@@ -193,6 +193,11 @@ jobs:
         cd language/jvm/src/test/python
         python validate_external_riddl.py --repo ${{ github.workspace }}/riddl-examples
 
+    - name: Verify GBNF is up-to-date
+      run: |
+        cd language/jvm/src/test/python
+        python ebnf_to_gbnf.py --check
+
   dependency-check:
     timeout-minutes: 15
     permissions: