fix: keep fail-closed per fact but stop zero-verified synthesis from emptying the whole brief

feat: multi-provider LLM support, prominent chat, design pass, and new analytics

fix: get_translation — exists check before init_db (matches get_brief pattern)

feat: storage/briefs_db.py — DB schema migration + translation cache

feat: Decision Stack redesign - 9 routes collapse into 4 (Verdict / Signals / Financials / Chat)

fix: remove redundant mkdir, guard corrupt JSON, tighten list_tickers sort test

feat: add briefs_db — persist last brief per ticker for portfolio Radar