feat: add COC↔LDS BOM mapping and expand canon support

Add cross-canon verse mapping between Community of Christ (COC/RLDS) and
LDS Book of Mormon versifications, with comprehensive test coverage.

Changes:
- Add mapping-loader.mjs with bidirectional lookup API
- Add COC↔LDS BOM mapping to RLDS _mapping.yml (8642 verses mapped)
- Add mapping generator scripts (generate-coc-lds-mapping.cjs)
- Add 79 mapping tests covering data integrity, critical paths, edge cases
- Add new canon data: RLDS, Buddhist, Hindu, Islam, Pseudo
- Add documentation and design docs
- Update .gitignore for dev artifacts (.claude/, test-results.md, etc.)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kckern

.gitignore

@@ -7,3 +7,8 @@ test_results/test_results.html
 /dist/*.cjs
 /dist/*.mjs
 /dist/*.map
+.env
+.claude/
+test-results.md
+.DS_Store
+.venv/