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/models/encounter.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 
-from sqlalchemy import DateTime, ForeignKey, SmallInteger, String, func
+from sqlalchemy import Boolean, DateTime, ForeignKey, SmallInteger, String, func, text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.core.database import Base
@@ -21,6 +21,7 @@ class Encounter(Base):
     current_pokemon_id: Mapped[int | None] = mapped_column(
         ForeignKey("pokemon.id"), index=True
     )
+    is_shiny: Mapped[bool] = mapped_column(Boolean, default=False, server_default=text("false"))
     caught_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now()
     )