Add evidence submission, 3-state offline tasks, parent comments, and retake policies

- Evidence on assignments: photo upload + notes + student self-note (needs help / not sure)
- Evidence required/optional/none flag per item; grading queue shows evidence with lightbox thumbnail
- Parent comment field when grading; shown to student on graded items
- Offline tasks: 3-state status (not started → in progress → done) with inline evidence form
- Retake policy per item: latest / highest / average — gradebook computes effective score accordingly
- Grading queue expanded to include lessons and practices (not just assignments) when evidence present

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

db.js

@@ -214,6 +214,15 @@ function tryAlter(sql) {
 tryAlter(`ALTER TABLE items ADD COLUMN due_date TEXT`);
 tryAlter(`ALTER TABLE items ADD COLUMN allow_retakes INTEGER NOT NULL DEFAULT 0`);
 tryAlter(`ALTER TABLE items ADD COLUMN prereq_item_id INTEGER`);
+tryAlter(`ALTER TABLE items ADD COLUMN evidence_mode TEXT NOT NULL DEFAULT 'none'`);
+tryAlter(`ALTER TABLE items ADD COLUMN retake_policy TEXT NOT NULL DEFAULT 'latest'`);
+tryAlter(`ALTER TABLE submissions ADD COLUMN evidence_notes TEXT`);
+tryAlter(`ALTER TABLE submissions ADD COLUMN evidence_photo TEXT`);
+tryAlter(`ALTER TABLE submissions ADD COLUMN student_note TEXT`);
+tryAlter(`ALTER TABLE submissions ADD COLUMN parent_comment TEXT`);
+tryAlter(`ALTER TABLE schedule ADD COLUMN status TEXT NOT NULL DEFAULT 'not_started'`);
+tryAlter(`ALTER TABLE schedule ADD COLUMN evidence_notes TEXT`);
+tryAlter(`ALTER TABLE schedule ADD COLUMN evidence_photo TEXT`);
 
 export const sha256 = (s) => createHash('sha256').update(String(s)).digest('hex');