Add group/course labels to spelling lists and flashcard decks

- group_name column added to lists and decks tables
- GET/POST/PUT endpoints for both include group_name
- Admin Spelling and Flashcards panels render items grouped under
  labeled section headers (e.g. Bible 6, Bible 8) with ungrouped
  items shown last
- Group input in each form has datalist autocomplete from existing groups
- Edit/copy populates the group field; Clear resets it

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

db.js

@@ -228,6 +228,8 @@ tryAlter(`ALTER TABLE students ADD COLUMN theme TEXT NOT NULL DEFAULT 'blue'`);
 tryAlter(`ALTER TABLE students ADD COLUMN streak_date TEXT`);
 tryAlter(`ALTER TABLE students ADD COLUMN streak_count INTEGER NOT NULL DEFAULT 0`);
 tryAlter(`ALTER TABLE students ADD COLUMN best_streak INTEGER NOT NULL DEFAULT 0`);
+tryAlter(`ALTER TABLE lists ADD COLUMN group_name TEXT NOT NULL DEFAULT ''`);
+tryAlter(`ALTER TABLE decks ADD COLUMN group_name TEXT NOT NULL DEFAULT ''`);
 
 export const sha256 = (s) => createHash('sha256').update(String(s)).digest('hex');