Add LDA topic inference — show detected topic label + defining words in UI

Add ML model comparison panel showing BoW, TF-IDF, Naive Bayes, and LDA results

Remove Firebase/Firestore from backend — use local JSON persistence only

feat: extension button placement, text extraction, OCR display + ML improvements

fix: cold start 502, favicon, verify state persistence

feat: Firebase integration — Firestore persistence, firebase.json hosting + Cloud Run rewrite

feat: PhilVerify Phase 1-3 — FastAPI backend, NLP pipeline, TF-IDF classifier (23/23 tests)