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/058_generation_strategy.sql

@@ -0,0 +1,8 @@
+-- Migration 058: Add generation_strategy column to canonical_controls
+-- Tracks whether a control was generated with document-grouped or ungrouped batching
+
+ALTER TABLE canonical_controls
+    ADD COLUMN IF NOT EXISTS generation_strategy TEXT NOT NULL DEFAULT 'ungrouped';
+
+COMMENT ON COLUMN canonical_controls.generation_strategy IS
+    'How chunks were batched during generation: ungrouped (random), document_grouped (by regulation+article)';