Add Let's Go Pikachu/Eevee encounter data

This PR adds encounter data for Pokemon Let's Go Pikachu and Let's Go Eevee
(version IDs 31 and 32, version group 19).

## Changes

### New Encounter Methods (IDs 38-41)
- `overworld` (38): Pokemon visible in the overworld on land
- `overworld-water` (39): Pokemon visible on water surface
- `overworld-flying` (40): Pokemon visible in the sky
- `rare-spawn` (41): Rare spawn after catch combo

### New Location Areas
- 35 new location areas for LGPE-specific encounters in Kanto

### Encounter Data
- 1,226 new encounter records covering all Kanto locations:
  - Routes 1-25
  - Viridian Forest, Mt. Moon, Rock Tunnel
  - Pokemon Tower, Seafoam Islands, Pokemon Mansion
  - Victory Road, Cerulean Cave
  - Power Plant, Diglett's Cave

### Data Sources
- Bulbapedia encounter tables for Let's Go Pikachu/Eevee
- Cross-referenced with Serebii for validation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: DJ-Meyers

data/v2/csv/encounter_method_prose.csv

@@ -78,3 +78,7 @@ encounter_method_id,local_language_id,name
 30,5,En utilisant le Devon Scope
 31,9,Fishing in a Feebas Tile
 31,5,En pêchant sur une tuile à Barpau
+38,9,Walking in the overworld
+39,9,Surfing in the overworld
+40,9,Flying Pokemon in the sky
+41,9,Rare spawn after catch combo

data/v2/csv/encounter_methods.csv

@@ -36,3 +36,7 @@ id,identifier,order
 35,berry-piles,35
 36,npc-trade,36
 37,sos-from-bubbling-spot,37
+38,overworld,38
+39,overworld-water,39
+40,overworld-flying,40
+41,rare-spawn,41

data/v2/csv/encounter_slots.csv

@@ -1171,3 +1171,7 @@ id,version_group_id,encounter_method_id,slot,rarity
 1170,28,18,,100
 1171,28,20,,100
 1172,28,21,,100
+1173,19,38,,100
+1174,19,39,,100
+1175,19,40,,100
+1176,19,41,,100