Add OpenAI-compatible LLM client service (v0.19.0)

LlmService wraps the local OpenAI-compatible server (default
http://192.168.1.70:1111/v1, no auth) with native fetch only — no new
dependencies. listModels() -> data[].id; chat(messages, opts?) ->
choices[0].message.content (non-2xx throws with status + body snippet);
summarize(text) = chat() with a concise-summary system prompt.

Env: LLM_API_BASE / LLM_MODEL (qwen3.8-27b) / LLM_TIMEOUT_MS (60000,
AbortSignal.timeout). Plain feature module wired into app.module.ts;
docs synced (AGENTS.md, README env list).

README.md

@@ -125,6 +125,9 @@ Config lives in `.env` (gitignored) and is passed via compose environment — cr
 - `MESH_DB_PATH` (default `./data/mesh-bot.db`) — SQLite file backing the message history (parent dir created if missing; in Docker, mounted at `/app/data` via a named volume so it survives container recreation)
 - `MESH_POLL_MS` (default `1000`) — how often the poller re-upserts the message history into SQLite and prunes rows beyond the newest 1000
 - `PORT` (default `3000`) — HTTP listen port
+- `LLM_API_BASE` (default `http://192.168.1.70:1111/v1`) — OpenAI-compatible LLM server base URL used by the in-process `LlmService` (`src/llm`; no auth)
+- `LLM_MODEL` (default `qwen3.8-27b`) — model id sent to `/chat/completions`
+- `LLM_TIMEOUT_MS` (default `60000`) — per-request timeout for LLM calls (the local 27B model can be slow)
 
 Note: the serial bridge accepts only ONE client at a time — if another app is
 connected to the radio, this bot will not get a connection.