Apply styled UI updates to app.py

Update README and Sidebar UI

Complete per-user data isolation, bug fixes, and Admin wipe trigger

fix: change OAuth links target to _blank to bypass HF iframe sandbox

fix: change OAuth links target to _top to break out of HF iframe (fixes 403/blank screen)

feat: rebuild auth from scratch using pure Firebase REST API

fix: make Streamlit startup resilient - handle import failures gracefully

feat: replace Firebase JS SDK with REST API + Google/GitHub OAuth redirect flow

Fix Firebase auth: replace iframe with native Streamlit login form (REST API)

Add Firebase auth login page (Google, GitHub, Email/Password) with FirebaseUI

Add Paste Text feature and restore disabled YouTube UI

Gracefully disable YouTube in Cloud Mode

feat: use Invidious API for YouTube transcripts

feat: browser-side YouTube transcript fetching

Replace YouTube fetch with timedtext API - no API keys needed, works from any server

Add YouTube Data API v3 for cloud-reliable transcript fetching with local fallback

Add auto-generated caption support for YouTube: multi-priority fetch, shorts URLs, transcript cleanup

Add OCR fallback for scanned/image PDFs using pytesseract + pdf2image

feat: Enable YouTube URLs in cloud with youtube-transcript-api

fix: Add missing os import for environment variable check

fix: Disable URL/YouTube ingestion in cloud mode (HF Spaces network restrictions)

Add multi-user support with session-based student IDs

Fix: Implement automatic date/day progression system

Fix: Restore except block that was accidentally removed during cleanup

Production code cleanup - remove debug statements and duplicates

Add data persistence and comprehensive citation system

Major improvements: Multi-subject plan generation, enhanced quiz/lesson quality, fixed UI layout

feat: Implement AI Plan Generator (Lite Mode) and Focus Mode Layout

Update backend RAG logic, app UI, and add documentation

feat: Implement initial Streamlit application with custom theming, extensive CSS, and an analytics dialog.