Add version groups to share routes and boss battles across games

Routes and boss battles now belong to a version_group instead of
individual games, so paired versions (e.g. Red/Blue, Gold/Silver)
share the same route structure and boss battles. Route encounters
gain a game_id column to support game-specific encounter tables
within a shared route. Includes migration, updated seeds, API
changes, and frontend type updates.

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

frontend/src/pages/RunEncounters.tsx

@@ -1093,9 +1093,9 @@ export function RunEncounters() {
                           .map((bp) => (
                             <div key={bp.id} className="flex items-center gap-1">
                               {bp.pokemon.spriteUrl ? (
-                                <img src={bp.pokemon.spriteUrl} alt={bp.pokemon.name} className="w-10 h-10" />
+                                <img src={bp.pokemon.spriteUrl} alt={bp.pokemon.name} className="w-20 h-20" />
                               ) : (
-                                <div className="w-10 h-10 bg-gray-200 dark:bg-gray-700 rounded-full" />
+                                <div className="w-20 h-20 bg-gray-200 dark:bg-gray-700 rounded-full" />
                               )}
                               <span className="text-xs text-gray-500 dark:text-gray-400">
                                 Lvl {bp.level}