Restrict transfers to HoF team and prevent blocking starter route

Transfer modal now only appears when a Hall of Fame team is selected,
using the existing hofTeam data instead of the survivors endpoint.
Without a HoF selection, advance proceeds directly with no transfer step.

Transferred encounters are now a separate category: they appear in their
own "Transferred Pokemon" section, don't occupy route slots in the
encounter map, and don't block the route-lock check (excluded via
genlocke_transfers subquery). The run detail endpoint returns
transferEncounterIds so the frontend can distinguish them.

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

backend/src/app/api/encounters.py

@@ -8,6 +8,7 @@ from sqlalchemy.orm import joinedload, selectinload
 from app.core.database import get_session
 from app.models.encounter import Encounter
 from app.models.evolution import Evolution
+from app.models.genlocke_transfer import GenlockeTransfer
 from app.models.genlocke import GenlockeLeg
 from app.models.nuzlocke_run import NuzlockeRun
 from app.models.pokemon import Pokemon
@@ -85,11 +86,14 @@ async def create_encounter(
             sibling_ids = [s.id for s in siblings]
 
         # Check if any relevant sibling already has an encounter in this run
+        # Exclude transfer-target encounters so they don't block the starter
+        transfer_target_ids = select(GenlockeTransfer.target_encounter_id)
         existing_encounter = await session.execute(
             select(Encounter)
             .where(
                 Encounter.run_id == run_id,
                 Encounter.route_id.in_(sibling_ids),
+                ~Encounter.id.in_(transfer_target_ids),
             )
         )
         if existing_encounter.scalar_one_or_none() is not None: