[UX] Skill autocomplete doesn't include namespace prefix, requiring Tab to expand before Enter

Description

When typing / and selecting a skill from the autocomplete menu, pressing Enter autocompletes the skill name but not the namespace prefix. For example, selecting zip-shell inserts /zip-shell instead of /global:zip-shell. Since the unprefixed form doesn't resolve, the skill doesn't invoke.

You have to Tab first (which expands to the fully-qualified /global:zip-shell), then Enter to invoke. The natural flow of filtering + Enter should just work.

Repro

1. Type /zip in the chat input (either standalone or as part of a larger message)
2. Autocomplete shows zip-shell as a suggestion
3. Press Enter on the highlighted suggestion
4. Input becomes /zip-shell (missing the global: prefix), which doesn't resolve
5. Workaround: press Tab instead of Enter to expand to /global:zip-shell, then Enter

Expected

Enter on an autocomplete suggestion should insert the fully-qualified name (/global:zip-shell) so the skill resolves immediately. This should work whether the slash command is the entire message or part of a larger prompt (e.g. write a /global:zip-shell script that checks X).

Actual

Enter inserts the short name without the namespace prefix. The skill doesn't resolve until you manually Tab-expand it first.

Environment

• macOS (Desktop app / CLI)
• Claude Code latest

Notes

Related closed issue: #54829 (same symptom on Windows, stale-closed).