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>

tools/import-pokedb/import_pokedb/mappings.py

@@ -84,8 +84,8 @@ ENCOUNTER_METHOD_MAP: dict[str, str] = {
     "cave-spot": "walk",
     "bubble-spot": "surf",
     "sand-spot": "walk",
-    "horde": "walk",
-    "sos-encounter": "walk",
+    "horde": "horde",
+    "sos-encounter": "sos",
     "ambush": "walk",
     # Seaweed / diving
     "diving": "surf",
@@ -105,7 +105,7 @@ ENCOUNTER_METHOD_MAP: dict[str, str] = {
     "dust-cloud": "walk",
     "hidden-grotto": "static",
     "hidden-encounter": "walk",
-    "horde-encounter": "walk",
+    "horde-encounter": "horde",
     "shaking-trees": "walk",
     "shaking-ore-deposits": "walk",
     "island-scan": "static",