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/alembic/versions/c3d4e5f6a7b8_add_route_grouping.py

@@ -0,0 +1,35 @@
+"""add parent_route_id for route grouping
+
+Revision ID: c3d4e5f6a7b8
+Revises: b2c3d4e5f6a7
+Create Date: 2026-02-06 12:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'c3d4e5f6a7b8'
+down_revision: Union[str, Sequence[str], None] = 'b2c3d4e5f6a7'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'routes',
+        sa.Column(
+            'parent_route_id',
+            sa.Integer(),
+            sa.ForeignKey('routes.id', ondelete='CASCADE'),
+            nullable=True,
+            index=True,
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('routes', 'parent_route_id')