Add game data seeding from PokeAPI with level ranges

Seed the database with Pokemon game data for 5 games (FireRed, LeafGreen,
Emerald, HeartGold, SoulSilver) using pokebase. Includes Alembic migrations
for route unique constraints and encounter level ranges, a two-phase seed
system (offline fetch to JSON, then idempotent upserts), and Dockerfile
updates for the seed runner.

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

backend/src/app/seeds/data/games.json

@@ -0,0 +1,37 @@
+[
+  {
+    "name": "Pokemon FireRed",
+    "slug": "firered",
+    "generation": 3,
+    "region": "kanto",
+    "release_year": 2004
+  },
+  {
+    "name": "Pokemon LeafGreen",
+    "slug": "leafgreen",
+    "generation": 3,
+    "region": "kanto",
+    "release_year": 2004
+  },
+  {
+    "name": "Pokemon Emerald",
+    "slug": "emerald",
+    "generation": 3,
+    "region": "hoenn",
+    "release_year": 2005
+  },
+  {
+    "name": "Pokemon HeartGold",
+    "slug": "heartgold",
+    "generation": 4,
+    "region": "johto",
+    "release_year": 2010
+  },
+  {
+    "name": "Pokemon SoulSilver",
+    "slug": "soulsilver",
+    "generation": 4,
+    "region": "johto",
+    "release_year": 2010
+  }
+]