Enforce Dupes Clause and Shiny Clause rules

Dupes Clause greys out Pokemon in the encounter modal whose evolution
family has already been caught, preventing duplicate selections. Shiny
Clause adds a dedicated Shiny Box and lets shiny catches bypass the
one-per-route lock via a new is_shiny column on encounters and a
/pokemon/families endpoint that computes evolution family groups.

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

backend/src/app/alembic/versions/b1c2d3e4f5a6_add_is_shiny_to_encounters.py

@@ -0,0 +1,29 @@
+"""add is_shiny to encounters
+
+Revision ID: b1c2d3e4f5a6
+Revises: f6a7b8c9d0e1
+Create Date: 2026-02-07 18:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'b1c2d3e4f5a6'
+down_revision: Union[str, Sequence[str], None] = 'f6a7b8c9d0e1'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'encounters',
+        sa.Column('is_shiny', sa.Boolean(), nullable=False, server_default=sa.text('false')),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('encounters', 'is_shiny')