Support per-directory output style configuration

Problem

Claude Code's output style (verbosity, formatting, tone) can only be configured globally. There's no way to set different output styles for different projects/directories.

Use Case

Developers often have varying expertise across domains. For example, a senior frontend engineer learning backend development would benefit from:

• Concise/minimal output in frontend projects (where explanations aren't needed)
• Explanatory/learning-oriented output in backend projects (where context and reasoning help)

Currently, the only workaround is adding style instructions to each project's CLAUDE.md, which is indirect and doesn't use the first-class output style system.

Proposal

Support output style configuration at the project level, e.g. via .claude/settings.json. This would allow setting the output style (concise, explanatory, etc.) per directory, complementing the existing global setting.