feat(acquisition): add category grouping for acquisition methods

Add category field to acquisition_methods table with 'General' default
Group acquisition methods by category in item and recipe detail views
Enable category management in admin configuration

backend/db/schema.sql

@@ -1169,6 +1169,7 @@ CREATE TABLE IF NOT EXISTS pokemon_favorite_things (
 CREATE TABLE IF NOT EXISTS acquisition_methods (
   id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
   name text NOT NULL UNIQUE,
+  category text NOT NULL DEFAULT 'General',
   sort_order integer NOT NULL DEFAULT 0 CHECK (sort_order >= 0),
   created_by_user_id integer REFERENCES users(id) ON DELETE SET NULL,
   updated_by_user_id integer REFERENCES users(id) ON DELETE SET NULL,
@@ -1565,6 +1566,9 @@ ALTER TABLE environments
 ALTER TABLE favorite_things
   ADD COLUMN IF NOT EXISTS opposite_favorite_thing_id integer;
 
+ALTER TABLE acquisition_methods
+  ADD COLUMN IF NOT EXISTS category text NOT NULL DEFAULT 'General';
+
 DO $$
 BEGIN
   IF NOT EXISTS (