Add GEDCOM import/export

A pragmatic GEDCOM parser + mapper: import reads INDI/FAM/SOUR and creates people, names, life events, partnership + qualified parent-child relationships, marriage events, places (deduped), sources, and citations from SOUR refs — returning a mapping report (counts + unmapped tags). Export serializes the tree back to GEDCOM (families derived from the edge model). Import is additive (no merge) and runs inline for now. Round-trip test passes; 29 tests total.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/api/v1/__init__.py

@@ -6,6 +6,7 @@ from app.api.v1 import (
     auth,
     citations,
     events,
+    gedcom,
     media,
     persons,
     relationships,
@@ -24,3 +25,4 @@ api_router.include_router(relationships.router)
 api_router.include_router(sources.router)
 api_router.include_router(citations.router)
 api_router.include_router(media.router)
+api_router.include_router(gedcom.router)