Add spelling test correction feature for admins

Adds a "Correct" button to each test in the Spelling Test History table.
Clicking it opens a modal showing each word, what the student typed, and a
checkbox to mark it correct or incorrect. Saving PATCHes the server, which
updates test_answers, recalculates the test score, and keeps any linked
course submission in sync.

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

db.js

@@ -242,6 +242,7 @@ tryAlter(`ALTER TABLE students ADD COLUMN young_learner INTEGER NOT NULL DEFAULT
 tryAlter(`ALTER TABLE students ADD COLUMN birthday TEXT`);
 tryAlter(`ALTER TABLE lists ADD COLUMN group_name TEXT NOT NULL DEFAULT ''`);
 tryAlter(`ALTER TABLE decks ADD COLUMN group_name TEXT NOT NULL DEFAULT ''`);
+tryAlter(`ALTER TABLE tests ADD COLUMN item_id INTEGER`);
 
 export const sha256 = (s) => createHash('sha256').update(String(s)).digest('hex');