Add chat title rename tool

[plux]

Description

Users can ask an agent to rename the current chat title, but ECA did not expose a native tool for that action. The only title changes came from client-side commands or automatic title generation.

This PR adds an approved native tool for chat title rename requests. It also makes title updates safe when automatic title generation, prompt cleanup saves, and manual renames happen near the same time.

Changes

• Add a rename_chat_title native tool that renames the current chat after the user explicitly asks for it.
• Reuse the existing chat title sanitization behavior for manual title updates, generated titles, and tool renames.
• Mark explicit title updates as custom so automatic title generation does not overwrite them.
• Serialize title update side effects and save current chat state to avoid stale prompt saves overwriting renamed titles on disk.
• Guard generated title updates with prompt id and prompt count so older title futures cannot overwrite newer generated titles.
• Exclude rename_chat_title from subagent tool sets because subagents do not own the visible parent chat title.
• Document the new tool in the changelog, tool configuration docs, feature docs, and protocol docs.
• Add regression coverage for rename validation, deleted-chat races, generated-title ordering, and title persistence races.

CI fix

I updated integration-test/integration/chat/commands_test.clj to include the upstream /plugin-update command and the current /plugin-uninstall argument description to fix failing integration tests.
Added as a separate commit 05748243f

[zikajk]

@plux If the user has to explicitly ask to rename the chat, wouldn’t it be easier for them to just rename it themselves? Or am I missing anything?