feat: merge document analysis into AI chat

feat: Document Analyzer, Persistent AI Memory, Multi-language (EN/HI/MR), Dark/Light Theme

feat: persistent AI chat with multi-session history sidebar

feat: AI Coach Mode, Fraud Explanations, Monthly Narrative — 3 new intelligence features

fix: resolve AI assistant page client crash by converting to HTTP streaming fallback, passing env vars to supervisord, and add payments feature

feat: login/register page, auth guard, working logout, real user identity, fraud detection UI, remove hardcoded API key

Fix: Unignore and track frontend/src/ directory in Git