Add per-condition encounter rates to seed data

Add a `condition` column to RouteEncounter so encounters can store
per-condition rates (time of day, season, weather) instead of flattening
to max(). Update the seed loader, API schemas, and frontend to support
the new `conditions` dict format in seed JSON.

Port the PoC branch's condition-aware EncounterModal UI with filter
tabs that let players see encounter rates for specific conditions.
Add horde/SOS as distinct encounter methods with their own badges.

Update the import tool to extract per-condition rates instead of
flattening, and add a merge script (tools/merge-conditions.py) that
enriches existing curated seed files with condition data from PokeDB.

Seed data updated for 22 games (5,684 encounters):
- Gen 2: Gold, Silver, Crystal (morning/day/night)
- Gen 4: HG, SS, Diamond, Pearl, Platinum, BD, SP (morning/day/night)
- Gen 5: Black, White, Black 2, White 2 (spring/summer/autumn/winter)
- Gen 7: Sun, Moon, Ultra Sun, Ultra Moon (day/night)
- Gen 8: Sword, Shield (weather)

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

backend/src/app/api/pokemon.py

@@ -213,6 +213,7 @@ async def get_pokemon_encounter_locations(
                 route_name=enc.route.name,
                 encounter_method=enc.encounter_method,
                 encounter_rate=enc.encounter_rate,
+                condition=enc.condition,
                 min_level=enc.min_level,
                 max_level=enc.max_level,
             )