feat(control-library): document-grouped batching, generation strategy tracking, sort by source

- Group chunks by regulation_code before batching for better LLM context
- Add generation_strategy column (ungrouped=v1, document_grouped=v2)
- Add v1/v2 badge to control cards in frontend
- Add sort-by-source option with visual group headers
- Add frontend page tests (18 tests)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/migrations/057_processing_path_batch.sql

@@ -0,0 +1,23 @@
+-- 057: Add batch processing paths to canonical_processed_chunks
+-- New values: structured_batch, llm_reform_batch (used by batch control generation)
+
+DO $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'canonical_processed_chunks') THEN
+        ALTER TABLE canonical_processed_chunks
+            DROP CONSTRAINT IF EXISTS canonical_processed_chunks_processing_path_check;
+        ALTER TABLE canonical_processed_chunks
+            ADD CONSTRAINT canonical_processed_chunks_processing_path_check
+            CHECK (processing_path IN (
+                'structured',
+                'llm_reform',
+                'skipped',
+                'prefilter_skip',
+                'no_control',
+                'store_failed',
+                'error',
+                'structured_batch',
+                'llm_reform_batch'
+            ));
+    END IF;
+END $$;