[BUG] Azure Cosmos NoSQL full-text filters match with default locale

Problem

FullTextContains, FullTextContainsAll and FullTextContainsAny lowercase both the document text and the search terms with the default locale (toLowerCase()). Under a Turkish/Azeri default locale the lowercased forms no longer match the indexed text: e.g. term PIN lowercases to pın and silently fails to match documents containing pin, breaking full-text retrieval.

Expected behavior

Both sides are lowercased with Locale.ROOT so matching is locale-independent.

Environment

langchain4j main (31950454f), module langchain4j-azure-cosmos-nosql.