POST /api/cases lets the frontend actually create a new dava dosyası
(no working "Yeni Dosya" flow existed before). chatMessage now
generates a short title from a case's first message (like Claude/
ChatGPT auto-titling) and renames the case, returned as `newTitle`.
Frontend's chat history trash icon was calling this endpoint but it
didn't exist yet, causing a JSON-parse error on the default 404 page.
Also renames the LegalOS health-check message to AyrisLegal.
requireAuth treated every chat caseId as a real cases row and rejected
"general" (the no-file chat sentinel) with 403. general chat now skips
the ownership check and is answered without touching chat_messages,
since that table's case_id is a NOT NULL FK to cases.
mstfyldz