[FEATURE] Team/group-scoped managed settings: per-team CLAUDE.md, permissions, and skills within an org

## Feature request

Allow enterprise admins to scope managed settings, CLAUDE.md instructions, and skills/plugins to **teams or groups** within an organization, instead of one org-wide blob.

## Problem

Server-managed settings (claude.ai admin console) currently deliver a single configuration to every Claude Code session in the org. That is perfect for universal guardrails (permission deny rules, company writing style), but organizations have teams with very different needs:

- Engineering needs rich context: architecture tables, repo conventions, infrastructure guardrails, domain skills.
- Non-engineering Claude Code users (ops, support, sales engineers) should not carry that content in every session. It wastes context tokens and can be confusing or irrelevant.
- Some instructions should be *enforced* for one team but not exist for another (for example, production read-only CLI rules for the platform team).

## Current workaround

We centralize an engineering CLAUDE.md in a git repo and each engineer adds an `@path` import line to their personal `~/.claude/CLAUDE.md`. This works but is opt-in: membership is defined by who remembered to add the line, there is no enforcement, and a misconfigured machine silently loses the whole layer. Skills have the same problem: they are discovered per-directory, so team-wide skill distribution relies on symlinks or plugin installs that each user must perform.

## Proposal

In Admin Settings > Claude Code, allow managed settings entries to target a group/workspace (reusing the existing claude.ai workspace or group concepts):

- Per-team `claudeMd` content, layered on top of the org-wide block.
- Per-team `permissions` (deny/allow) and hooks.
- Per-team skill/plugin assignment so members automatically get the team's skills on login, kept up to date.
- Precedence: org-wide managed > team managed > user/project/local, with deny rules merging across levels.

## Impact

This would let enterprises truly enforce differentiated Claude behavior across teams, replace fragile per-user import conventions, and make team onboarding zero-step: log in, get your team's instructions, guardrails, and skills.

Context: we are an industrial IoT platform company rolling out org-wide guardrails via managed settings today; the single-scope limitation is the one gap forcing us to keep a parallel opt-in distribution mechanism for engineering context.

No files, tests, or entry points are named in the issue. Start by locating the existing org-wide managed-settings delivery and workspace or group membership handling. Done means team-targeted CLAUDE.md, permissions, hooks, and skill/plugin assignments follow the stated precedence and merging rules, with coverage for team and org scopes.

索引モデルが issue の本文から書いたものです。