Add bulk import for evolutions, routes, and bosses

Add three new bulk import endpoints that accept the same JSON format as
their corresponding export endpoints, enabling round-trip compatibility:

- POST /evolutions/bulk-import (upsert by from/to pokemon pair)
- POST /games/{id}/routes/bulk-import (reuses seed loader for hierarchy)
- POST /games/{id}/bosses/bulk-import (reuses seed loader with team data)

Generalize BulkImportModal to support all entity types with configurable
title, example, and result labels. Wire up Bulk Import buttons on
AdminEvolutions, and AdminGameDetail routes/bosses tabs.

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

backend/src/app/schemas/pokemon.py

@@ -158,3 +158,60 @@ class EvolutionUpdate(CamelModel):
     held_item: str | None = None
     condition: str | None = None
     region: str | None = None
+
+
+# --- Bulk import schemas (match export format, snake_case) ---
+
+
+class BulkEvolutionItem(BaseModel):
+    from_pokeapi_id: int
+    to_pokeapi_id: int
+    trigger: str
+    min_level: int | None = None
+    item: str | None = None
+    held_item: str | None = None
+    condition: str | None = None
+    region: str | None = None
+
+
+class BulkRouteEncounterItem(BaseModel):
+    pokeapi_id: int
+    method: str
+    encounter_rate: int
+    min_level: int
+    max_level: int
+
+
+class BulkRouteChildItem(BaseModel):
+    name: str
+    order: int
+    pinwheel_zone: int | None = None
+    encounters: list[BulkRouteEncounterItem] = []
+
+
+class BulkRouteItem(BaseModel):
+    name: str
+    order: int
+    encounters: list[BulkRouteEncounterItem] = []
+    children: list[BulkRouteChildItem] = []
+
+
+class BulkBossPokemonItem(BaseModel):
+    pokeapi_id: int
+    level: int
+    order: int
+
+
+class BulkBossItem(BaseModel):
+    name: str
+    boss_type: str
+    specialty_type: str | None = None
+    badge_name: str | None = None
+    badge_image_url: str | None = None
+    level_cap: int
+    order: int
+    after_route_name: str | None = None
+    location: str
+    section: str | None = None
+    sprite_url: str | None = None
+    pokemon: list[BulkBossPokemonItem] = []