Automatic chat naming titles chats 'Hello'/'Greeting' and never updates

Description

The new _chat_naming plugin (introduced in commit b6be345a) defaults to automatic_naming_mode: "once", which names a chat from only its first user message. When a chat starts with a greeting (e.g. "Hello!"), the Utility Model returns a generic 1-3 word name like "Hello" or "Greeting", and because once mode never renames, the chat keeps that title forever - even after the actual topic arrives.

Steps to reproduce

1. Start a new chat with "Hello!"
2. Ask a substantive question (e.g. "Help me refactor my Python project")
3. The chat remains titled "Hello"/"Greeting" indefinitely

Expected behavior

The title should reflect the actual conversation topic.

Environment

• Latest main (b1cbd1f9), _chat_naming plugin default config (automatic_naming_mode: once)
• Any provider; naming uses the Utility Model

Workaround

Create usr/plugins/_chat_naming/config.json with automatic_naming_mode: "always" (downside: one extra Utility Model call per turn).

Suggested fix

Keep once mode but defer naming until the first substantive user message (non-greeting, at least 3 words). This keeps the single Utility Model call while ensuring titles reflect real content. PR: #1896