Add Hall of Fame team selection for completed runs

After marking a run as completed, a modal prompts the player to select
which Pokemon (up to 6) entered the Hall of Fame. The selection is stored
as hof_encounter_ids on the run, displayed in the victory banner, and
can be edited later. This lays the foundation for scoping genlocke
retireHoF to only the actual HoF team.

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

backend/src/app/api/runs.py

@@ -120,6 +120,38 @@ async def update_run(
 
     update_data = data.model_dump(exclude_unset=True)
 
+    # Validate hof_encounter_ids if provided
+    if "hof_encounter_ids" in update_data and update_data["hof_encounter_ids"] is not None:
+        hof_ids = update_data["hof_encounter_ids"]
+        if len(hof_ids) > 6:
+            raise HTTPException(
+                status_code=400, detail="HoF team cannot have more than 6 Pokemon"
+            )
+        if hof_ids:
+            # Validate all encounter IDs belong to this run and are alive
+            enc_result = await session.execute(
+                select(Encounter).where(
+                    Encounter.id.in_(hof_ids),
+                    Encounter.run_id == run_id,
+                )
+            )
+            found = {e.id: e for e in enc_result.scalars().all()}
+            missing = [eid for eid in hof_ids if eid not in found]
+            if missing:
+                raise HTTPException(
+                    status_code=400,
+                    detail=f"Encounters not found in this run: {missing}",
+                )
+            not_alive = [
+                eid for eid, e in found.items()
+                if e.status != "caught" or e.faint_level is not None
+            ]
+            if not_alive:
+                raise HTTPException(
+                    status_code=400,
+                    detail=f"Encounters are not alive: {not_alive}",
+                )
+
     # Auto-set completed_at when ending a run
     if "status" in update_data and update_data["status"] in ("completed", "failed"):
         if run.status != "active":