Feature Request: Allow customizing auto-generated session/conversation titles (language & format)

Summary

Auto-generated session/conversation titles are always in English, even when language: "japanese" is set in settings.json. There is no way to control the language or format of session titles.

Problem

• The language setting in settings.json does not affect session title generation
• Session titles are always generated in English (e.g., "Create sessions for upcoming business meetings")
• For non-English users, this makes it very difficult to identify sessions at a glance
• There is no hook event or API to programmatically rename sessions

Desired Behavior

1. Respect language setting: When language is set (e.g., "japanese"), auto-generated session titles should be in that language
2. Custom format support: Allow users to define a title format template (e.g., {company}_{context}_{time}) via settings
3. Programmatic rename: Provide a tool or hook mechanism to rename sessions from within a conversation (not just the /rename CLI command)

Workaround Attempted

• Set language: "japanese" in ~/.claude/settings.json → No effect on session titles
• Added naming rules in CLAUDE.md → Not read before title generation
• SessionStart hook with systemMessage → Can only remind Claude to suggest /rename, user must manually copy-paste

Environment

• Claude Code CLI
• macOS