fix language confusion and hallucinations: centralized resolver + deterministic abstention

fix footer overlapping input: add 32px bottom padding to shell and login page

add security & privacy declaration footer to login and chat pages

major quality upgrade: 12 improvements across retrieval, citations, UX

feat: context budget packing, LLM classifier, reranker, multi-query, dual Excel ingestion

fix: improve retrieval depth and answer quality (4 fixes)

fix: reduce top_k to 4 and cap chunk chars to stay under Groq 6000 TPM limit

hide SQL query from chat response

fix SQL answer not shown; show Excel in documents list

make upload page scrollable

update empty chat message in FR and EN

initial