Add go-llm v1 chat Client with OpenAI-compatible and Ollama adapters.

Co-authored-by: Cursor <cursoragent@cursor.com>

CONTEXT.md

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+# go-llm
+
+Shared Go Library for calling a chat LLM: one Client interface with an Ollama-native Adapter and an OpenAI-compatible Adapter. ExApps and Services import `gitea.neitzel.de/konrad/go-llm`. It has no Nextcloud types and no story types.
+
+## Language
+
+**Client**:
+A configured caller bound to one Adapter, base URL, optional API key, and HTTP behaviour. Chat, Stream, and List Models go through that Client.
+_Avoid_: a chat-history store, Nextcloud AppAPI credentials
+
+**Adapter**:
+Which native protocol the Client speaks: Ollama (`/api/chat`) or OpenAI-compatible (`/v1/chat/completions`). vLLM and similar servers use the OpenAI-compatible Adapter.
+_Avoid_: a third vLLM-native protocol, one Adapter type per model name
+
+**Message**:
+One chat turn with a role (system, user, or assistant) and text content. The Library sends and streams Messages; it does not build product prompts.
+_Avoid_: Story, Chapter, prompt template
+
+**Stream**:
+The same Chat request delivered as incremental text chunks instead of one complete reply.
+_Avoid_: writing chunks to files
+
+**Model**:
+A server-side model name as listed by the Adapter. The Library lists names and accepts the name the caller passes; it does not download or install models.
+_Avoid_: GGUF files, Ollama Modelfile management