Add PokeDB sprite downloading (100x100 WebP)

Download pokemon sprites from PokeDB CDN during import, cached locally
as {pokeapi_id}.webp. Replaces PokeAPI GitHub sprite URLs. ~4.6MB for
all 1119 unique sprites.

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

tools/import-pokedb/import_pokedb/sprites.py

@@ -0,0 +1,78 @@
+"""Download and manage PokeDB pokemon sprites."""
+
+from __future__ import annotations
+
+import sys
+import urllib.request
+from pathlib import Path
+from typing import Any
+
+from .mappings import PokemonMapper
+
+
+def download_sprites(
+    pokemon_mapper: PokemonMapper,
+    encountered_form_ids: set[str],
+    sprites_dir: Path,
+) -> dict[str, str]:
+    """Download sprites for all encountered pokemon forms.
+
+    Returns a mapping of pokemon_form_identifier → local sprite filename.
+    Skips already-downloaded sprites.
+    """
+    sprites_dir.mkdir(parents=True, exist_ok=True)
+
+    to_download: list[tuple[str, str, Path]] = []  # (form_id, url, dest)
+    result: dict[str, str] = {}
+
+    for form_id in sorted(encountered_form_ids):
+        info = pokemon_mapper.lookup(form_id)
+        if info is None:
+            continue
+
+        pokeapi_id, _ = info
+        sprite_url = pokemon_mapper.get_sprite_url(form_id)
+        if not sprite_url:
+            continue
+
+        filename = f"{pokeapi_id}.webp"
+        dest = sprites_dir / filename
+        result[form_id] = filename
+
+        if not dest.exists():
+            to_download.append((form_id, sprite_url, dest))
+
+    if not to_download:
+        print(f"  Sprites: {len(result)} already cached")
+        return result
+
+    print(f"  Downloading {len(to_download)} sprites ({len(result) - len(to_download)} cached)...")
+
+    failed = 0
+    for i, (form_id, url, dest) in enumerate(to_download, 1):
+        try:
+            urllib.request.urlretrieve(url, dest)
+        except Exception as e:
+            print(f"  Warning: Failed to download sprite for {form_id}: {e}", file=sys.stderr)
+            failed += 1
+            # Remove the failed entry from results
+            result.pop(form_id, None)
+
+        # Progress every 100
+        if i % 100 == 0:
+            print(f"    {i}/{len(to_download)}...")
+
+    if failed:
+        print(f"  Sprites: {len(result)} downloaded, {failed} failed")
+    else:
+        print(f"  Sprites: {len(result)} total ({len(to_download)} new)")
+
+    return result
+
+
+def sprite_path_for_pokemon(pokeapi_id: int, sprites_dir_name: str = "sprites") -> str:
+    """Generate the relative sprite path for use in pokemon.json.
+
+    Returns a path like "sprites/25.webp" suitable for the sprite_url field.
+    """
+    return f"{sprites_dir_name}/{pokeapi_id}.webp"