GEDCOM: duplicate-aware import + typed name/attribute mapping

Duplicate detection (the "merge / skip / overwrite" the user asked for):
- New POST /gedcom/preview dry-runs the file and flags incoming people that
  resemble existing ones (name similarity via difflib + birth-year guard;
  high/medium score). No writes.
- /gedcom/import takes default_action (new|skip|merge|overwrite) + per-xref
  resolutions {xref: {action, target_id}}:
    new       create as a new person (current behavior)
    skip      link families to the existing person, copy nothing
    merge     attach the incoming names (as alternates), events, citations,
              and notes onto the existing person
    overwrite soft-delete the existing person, import the incoming one fresh
  Relationship creation is deduped so a merge can't double an edge.

Richer record mapping (covers the user's repo's GEDCOM):
- Multiple NAME records honor their TYPE; _MARNM (and NICK) import as typed
  alternate names — maiden stays primary, married becomes a "married" Name.
- RELI -> a "religion" event with the value in detail; OCCU/EDUC values too.
- NOTE -> person notes (and event notes); NOTE/RELI are no longer "unmapped".
- Export round-trips name TYPE.

Verified against the user's 2185-person export: 0 unmapped tags. 48 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/v1/gedcom.py

@@ -1,25 +1,56 @@
+import json
 import uuid
 
-from fastapi import APIRouter, File, Response, UploadFile
+from fastapi import APIRouter, File, Form, Response, UploadFile
 
 from app.api.deps import CurrentUser, SessionDep
-from app.schemas.gedcom import ImportReport
+from app.schemas.gedcom import ImportPreview, ImportReport
 from app.services import gedcom, tree_service
 
 router = APIRouter(prefix="/trees", tags=["gedcom"])
 
 
+@router.post("/{tree_id}/gedcom/preview", response_model=ImportPreview)
+async def preview_gedcom(
+    tree_id: uuid.UUID,
+    session: SessionDep,
+    current: CurrentUser,
+    file: UploadFile = File(...),
+) -> ImportPreview:
+    """Dry run: report counts and incoming people that look like duplicates of
+    existing ones, so the user can choose how to resolve each before importing."""
+    tree = await tree_service.get_tree(session, viewer_id=current.id, tree_id=tree_id)
+    text = (await file.read()).decode("utf-8", errors="replace")
+    report = await gedcom.preview_gedcom(session, actor=current, tree=tree, text=text)
+    return ImportPreview(**report)
+
+
 @router.post("/{tree_id}/gedcom/import", response_model=ImportReport)
 async def import_gedcom(
     tree_id: uuid.UUID,
     session: SessionDep,
     current: CurrentUser,
     file: UploadFile = File(...),
+    default_action: str = Form("new"),
+    resolutions: str = Form("{}"),
 ) -> ImportReport:
-    # NOTE: additive — records are created as new; existing people are not merged.
+    """Import a GEDCOM. ``default_action`` (new|skip|merge|overwrite) applies to
+    incoming people that match an existing one; ``resolutions`` is a JSON object
+    {xref: {action, target_id}} overriding it per record."""
     tree = await tree_service.get_tree(session, viewer_id=current.id, tree_id=tree_id)
     text = (await file.read()).decode("utf-8", errors="replace")
-    report = await gedcom.import_gedcom(session, actor=current, tree=tree, text=text)
+    try:
+        parsed = json.loads(resolutions or "{}")
+    except json.JSONDecodeError:
+        parsed = {}
+    report = await gedcom.import_gedcom(
+        session,
+        actor=current,
+        tree=tree,
+        text=text,
+        default_action=default_action,
+        resolutions=parsed,
+    )
     return ImportReport(**report)