fix: QA audit — lint cleanup, i18n fixes, module visibility, sidebar UX

- Fix 97 lint errors → 0 (unused imports, params, variables across 40+ files)
- Fix i18n key format: colon → dot notation for next-intl compatibility
- Add missing i18n keys (routes.application, routes.home, confirm)
- Fix module visibility: sidebar now respects per-account DB features
- Fix inject function: use dot-notation keys, add collapsed:true defaults
- Fix ConfirmDialog: use useTranslations instead of hardcoded German defaults
- Fix events page: replace placeholder 'Beschreibung' with proper description
- Fix Dockerfile: add NEXT_PUBLIC_CI ARG for Docker builds
- Collapse secondary sidebar sections by default for cleaner UX

apps/e2e/tests/course-enrollment.spec.ts

@@ -1,11 +1,11 @@
 /**
  * E2E Test: Course Enrollment
  */
-import { test, expect } from '@playwright/test';
+import { test } from '@playwright/test';
 
 test.describe('Course Management', () => {
   test('create course, enroll participant, check capacity, waitlist', async ({
-    page,
+    page: _page,
   }) => {
     // Create course with capacity 2
     // Enroll participant 1 → status: enrolled
@@ -13,13 +13,13 @@ test.describe('Course Management', () => {
     // Enroll participant 3 → status: waitlisted (capacity full)
   });
 
-  test('course calendar view shows sessions', async ({ page }) => {
+  test('course calendar view shows sessions', async ({ page: _page }) => {
     // Create course with sessions
     // Navigate to calendar
     // Verify sessions visible
   });
 
-  test('attendance tracking', async ({ page }) => {
+  test('attendance tracking', async ({ page: _page }) => {
     // Create course + session + participants
     // Mark attendance
     // Verify attendance persists