Claude agent: ensure workspace `.claude/skills` are loaded (don't hardcode bare mode)

[atsushi-ishibashi]

Request

• Ensure the packaged Claude agent loads .claude/skills/ from the session workspace.
• If the adapter runs the CLI in a bare-like mode that skips skill scanning, make that configurable per session (session option, ACP config option, or agent-package env var), defaulting to current behavior.
• A regression test asserting that a workspace skill is visible to the model would lock this in.

Why

Project-level skills placed in the session workspace are a standard Claude Code extension point. If the CLI is launched in bare mode, .claude/skills/ is silently never scanned and there is no way to enable it from the client side — the skills just don't exist as far as the model is concerned, with no error anywhere.