fix: Corriger les 84 échecs E2E pré-existants

Les tests E2E échouaient pour trois raisons principales :

1. Initialisation asynchrone TipTap — L'éditeur rich-text s'initialise
   via des imports dynamiques dans onMount(). Les tests interagissaient
   avec .rich-text-content avant que l'élément n'existe dans le DOM.
   Ajout d'attentes explicites avant chaque interaction avec l'éditeur.

2. Pollution inter-tests — Les fonctions de nettoyage (classes, subjects)
   ne supprimaient pas les tables dépendantes (homework, evaluations,
   schedule_slots), provoquant des erreurs FK silencieuses dans les
   try/catch. De plus, homework_submissions n'a pas de ON DELETE CASCADE
   sur homework_id, nécessitant une suppression explicite.

3. État partagé du tenant — Les règles de devoirs (homework_rules) et le
   calendrier scolaire (school_calendar_entries avec Vacances de Printemps)
   persistaient entre les fichiers de test, bloquant la création de devoirs
   dans des tests non liés aux règles.

frontend/e2e/homework-richtext-attachments.spec.ts

@@ -105,8 +105,9 @@ async function createHomework(page: import('@playwright/test').Page, title: stri
 	await page.locator('#hw-subject').selectOption({ index: 1 });
 	await page.locator('#hw-title').fill(title);
 
-	// Type in WYSIWYG editor
+	// Type in WYSIWYG editor (TipTap initializes asynchronously)
 	const editorContent = page.locator('.modal .rich-text-content');
+	await expect(editorContent).toBeVisible({ timeout: 10000 });
 	await editorContent.click();
 	await page.keyboard.type('Consignes du devoir');
 
@@ -188,11 +189,30 @@ test.describe('Rich Text & Attachments (Story 5.9)', () => {
 	});
 
 	test.beforeEach(async () => {
+		// homework_submissions has NO CASCADE on homework_id — delete submissions first
+		try {
+			runSql(`DELETE FROM submission_attachments WHERE submission_id IN (SELECT hs.id FROM homework_submissions hs JOIN homework h ON hs.homework_id = h.id WHERE h.tenant_id = '${TENANT_ID}' AND h.teacher_id IN (SELECT id FROM users WHERE email = '${TEACHER_EMAIL}' AND tenant_id = '${TENANT_ID}'))`);
+		} catch { /* Table may not exist */ }
+		try {
+			runSql(`DELETE FROM homework_submissions WHERE homework_id IN (SELECT id FROM homework WHERE tenant_id = '${TENANT_ID}' AND teacher_id IN (SELECT id FROM users WHERE email = '${TEACHER_EMAIL}' AND tenant_id = '${TENANT_ID}'))`);
+		} catch { /* Table may not exist */ }
 		try {
 			runSql(`DELETE FROM homework WHERE tenant_id = '${TENANT_ID}' AND teacher_id IN (SELECT id FROM users WHERE email = '${TEACHER_EMAIL}' AND tenant_id = '${TENANT_ID}')`);
 		} catch {
 			// Table may not exist
 		}
+
+		// Disable any homework rules left by other test files (homework-rules-warning,
+		// homework-rules-hard) to prevent rule warnings blocking homework creation.
+		try {
+			runSql(`UPDATE homework_rules SET enabled = false, updated_at = NOW() WHERE tenant_id = '${TENANT_ID}'`);
+		} catch { /* Table may not exist */ }
+
+		// Clear school calendar entries that may block dates (Vacances de Printemps, etc.)
+		try {
+			runSql(`DELETE FROM school_calendar_entries WHERE tenant_id = '${TENANT_ID}'`);
+		} catch { /* Table may not exist */ }
+
 		clearCache();
 	});
 
@@ -231,8 +251,9 @@ test.describe('Rich Text & Attachments (Story 5.9)', () => {
 			await page.locator('#hw-subject').selectOption({ index: 1 });
 			await page.locator('#hw-title').fill('Devoir texte riche');
 
-			// Type in rich text editor
+			// Type in rich text editor (TipTap initializes asynchronously)
 			const editorContent = page.locator('.modal .rich-text-content');
+			await expect(editorContent).toBeVisible({ timeout: 10000 });
 			await editorContent.click();
 			await page.keyboard.type('Consignes importantes');
 
@@ -255,6 +276,7 @@ test.describe('Rich Text & Attachments (Story 5.9)', () => {
 			await page.locator('#hw-title').fill('Devoir gras test');
 
 			const editorContent = page.locator('.modal .rich-text-content');
+			await expect(editorContent).toBeVisible({ timeout: 10000 });
 			await editorContent.click();
 			await page.keyboard.type('Normal ');
 
@@ -459,8 +481,9 @@ test.describe('Rich Text & Attachments (Story 5.9)', () => {
 			await hwCard.getByRole('button', { name: /modifier/i }).click();
 			await expect(page.getByRole('dialog')).toBeVisible({ timeout: 10000 });
 
-			// WYSIWYG editor contains the old text
+			// WYSIWYG editor contains the old text (TipTap initializes asynchronously)
 			const editorContent = page.locator('.modal .rich-text-content');
+			await expect(editorContent).toBeVisible({ timeout: 10000 });
 			await expect(editorContent).toContainText('Ancienne description', { timeout: 5000 });
 		});
 	});