feat: add skill item drops configuration for pokemon

Add `has_item_drop` flag to skills and `pokemon_skill_item_drops` table
Enable configuring item drops for specific pokemon skills in editor
Show skill item drops on pokemon and item detail pages

backend/db/schema.sql

@@ -40,10 +40,12 @@ CREATE INDEX IF NOT EXISTS user_sessions_user_id_idx
 
 CREATE TABLE IF NOT EXISTS skills (
   id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
-  name text NOT NULL UNIQUE
+  name text NOT NULL UNIQUE,
+  has_item_drop boolean NOT NULL DEFAULT false
 );
 
 ALTER TABLE skills DROP COLUMN IF EXISTS subcategory;
+ALTER TABLE skills ADD COLUMN IF NOT EXISTS has_item_drop boolean NOT NULL DEFAULT false;
 CREATE UNIQUE INDEX IF NOT EXISTS skills_name_key ON skills(name);
 
 CREATE TABLE IF NOT EXISTS favorite_things (
@@ -154,6 +156,14 @@ CREATE TABLE IF NOT EXISTS item_favorite_things (
   PRIMARY KEY (item_id, favorite_thing_id)
 );
 
+CREATE TABLE IF NOT EXISTS pokemon_skill_item_drops (
+  pokemon_id integer NOT NULL,
+  skill_id integer NOT NULL,
+  item_id integer NOT NULL REFERENCES items(id),
+  PRIMARY KEY (pokemon_id, skill_id),
+  FOREIGN KEY (pokemon_id, skill_id) REFERENCES pokemon_skills(pokemon_id, skill_id) ON DELETE CASCADE
+);
+
 CREATE TABLE IF NOT EXISTS recipe_materials (
   recipe_id integer NOT NULL REFERENCES recipes(id) ON DELETE CASCADE,
   item_id integer NOT NULL REFERENCES items(id),