Add deterministic computed-ratios layer (Approach 2); FinanceBench 20% -> 45%

Fix stale '18-company' references (corpus is now 25; make eval text count-agnostic)

Expand corpus to 25 companies (add Apple, Alphabet, Amazon, NVIDIA, Tesla, JPMorgan, Walmart)

Update README + evals for 18-company EDGAR corpus; add capability eval (100%) alongside FinanceBench (20%)

Expand corpus to 18 companies (recent SEC 10-Ks); ship prebuilt index via git-lfs

FinChat: RAG chatbot over SEC 10-K filings