Add hierarchical route grouping for multi-area locations

Locations like Mt. Moon (with 1F, B1F, B2F floors) are now grouped so
only one encounter can be logged per location group, enforcing Nuzlocke
first-encounter rules correctly.

- Add parent_route_id column with self-referential FK to routes table
- Add parent/children relationships on Route model
- Update games API to return hierarchical route structure
- Add validation in encounters API to prevent parent route encounters
  and duplicate encounters within sibling routes (409 conflict)
- Update frontend with collapsible RouteGroup component
- Auto-derive route groups from PokeAPI location/location-area structure
- Regenerate seed data with 70 parent routes and 315 child routes

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

backend/src/app/api/encounters.py

@@ -1,7 +1,7 @@
 from fastapi import APIRouter, Depends, HTTPException, Response
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy.orm import joinedload
+from sqlalchemy.orm import joinedload, selectinload
 
 from app.core.database import get_session
 from app.models.encounter import Encounter
@@ -33,11 +33,45 @@ async def create_encounter(
     if run is None:
         raise HTTPException(status_code=404, detail="Run not found")
 
-    # Validate route exists
-    route = await session.get(Route, data.route_id)
+    # Validate route exists and load its children
+    result = await session.execute(
+        select(Route)
+        .where(Route.id == data.route_id)
+        .options(selectinload(Route.children))
+    )
+    route = result.scalar_one_or_none()
     if route is None:
         raise HTTPException(status_code=404, detail="Route not found")
 
+    # Cannot create encounter on a parent route (routes with children)
+    if route.children:
+        raise HTTPException(
+            status_code=400,
+            detail="Cannot create encounter on a parent route. Use a child route instead.",
+        )
+
+    # If this route has a parent, check if any sibling already has an encounter
+    if route.parent_route_id is not None:
+        # Get all sibling route IDs (routes with same parent, including this one)
+        siblings_result = await session.execute(
+            select(Route.id).where(Route.parent_route_id == route.parent_route_id)
+        )
+        sibling_ids = [r for r in siblings_result.scalars().all()]
+
+        # Check if any sibling already has an encounter in this run
+        existing_encounter = await session.execute(
+            select(Encounter)
+            .where(
+                Encounter.run_id == run_id,
+                Encounter.route_id.in_(sibling_ids),
+            )
+        )
+        if existing_encounter.scalar_one_or_none() is not None:
+            raise HTTPException(
+                status_code=409,
+                detail="This location group already has an encounter. Only one encounter per location group is allowed.",
+            )
+
     # Validate pokemon exists
     pokemon = await session.get(Pokemon, data.pokemon_id)
     if pokemon is None: