deploy: accept .docx and .pptx uploads

deploy: chat model picker + gpt-oss-120b default

deploy: hybrid retrieval + reranker

fix: 400 on chat_id misuse takes priority over 503

feat: chat history (multi-turn, search, rename, delete)

feat: RAG/web toggles, strict mode, Tavily search, chat settings

feat: video ingest support and error_message column

auth: collect first/last name at registration; nullable columns + migration

deploy phase 2 (auth: verification, reset, password rules, blocklist)

initial backend deploy