Plugin skill autocomplete displays flat names instead of namespaced format

Description

When using the / command autocomplete for plugin skills, the autocomplete UI displays skill names without their namespace prefix, even though the skills are correctly namespaced and invocable with the full format.

Steps to Reproduce

1. Install a plugin (e.g., hypothetical plugin named example-utils with skills format and validate)
2. Type /example-utils: in the Claude Code CLI
3. Observe the autocomplete dropdown

Expected Behavior

The autocomplete should display:

/example-utils:format    [example-utils] Format code files...
/example-utils:validate  [example-utils] Validate configuration...

Actual Behavior

The autocomplete displays:

/format    [example-utils] Format code files...
/validate  [example-utils] Validate configuration...

The namespace prefix example-utils: is missing from the command name column, even though:

• ✅ The plugin name appears in the description column as [example-utils]
• ✅ Typing /example-utils: correctly filters to show only those skills
• ✅ Invoking /example-utils:format works correctly

Impact

Confusion about naming conflicts: The flat display makes it appear that skills like /format exist at the global level, potentially conflicting with user-scoped skills of the same name.

Unclear invocation syntax: Users may not realize they need to use the namespaced format (/example-utils:format) when the autocomplete shows just /format.

Environment

• Claude Code CLI (latest version)
• Platform: Linux
• Observed with custom plugins installed via plugin marketplace

Suggested Fix

Update the autocomplete rendering logic to display the full namespaced command name (e.g., /example-utils:format) in the command name column when showing plugin skills.