feat(web): rewrite flashcard/quiz engine as Alpine.js components

Phase 2 of the sidebar consolidation. Replaces the 863-line vanilla JS
app.js with declarative Alpine components:

- reviewApp(defaultMode) factory: course grid, session config, card
  player (flashcard flip + quiz ABCD), session summary with retry
- Alpine.store('settings'): voice toggle, theme, dyslexic font —
  shared across all views, persisted to localStorage
- Both Flashcards and Quizzes sidebar tabs get independent reviewApp
  instances with x-show sub-navigation (courses → config → study →
  summary)
- Keyboard shortcuts via @keydown.window scoped to active tab
- Pomodoro timer preserved as global functions (Phase 3 Alpine-ifies)
- Service worker cache bumped to v6, removes session.html + app.js

app.js is now unused dead code (Phase 3 will delete it).

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

Author: NetDevAutomate