Add a setting to display raw skill identifiers #5

Allow users to choose raw skill identifiers such as create-pr-stack instead of display names such as Create PR stack.

Scope and acceptance:

• Add an appearance preference for display names versus raw identifiers.
• Apply it consistently to the skill picker, draft chips, and sent-message chips where supported.
• Preserve skill identity and invocation; changing the label must not select a different skill.
• Check web, desktop, and mobile and state any unsupported differences.

Upstream reference: pingdotgg#27741 preserves raw names when no provider display name exists, but does not provide this override setting. Review the current implementation before adding overlapping behavior.

Here, raw identifier means the skill slug or directory name, not the literal filename SKILL.md.