Skill tool fails to resolve short name when plugin and skill names match

Summary

Invoking a skill by its short name fails when the plugin name and skill name are identical. Skill("refine-issue") returns "Unknown skill: refine-issue" but Skill("refine-issue:refine-issue") works. The short form should resolve to the primary skill.

Steps to Reproduce

1. Install a plugin where the primary skill name matches the plugin name (e.g., refine-issue plugin with a skill named refine-issue)
2. The skill appears in the available skills list as refine-issue:refine-issue
3. Call Skill("refine-issue") → fails with "Unknown skill: refine-issue"
4. Call Skill("refine-issue:refine-issue") → works

Expected Behavior

Skill("refine-issue") should resolve to refine-issue:refine-issue when the plugin has a primary skill with the same name. This matches the naming convention that plugin:plugin is redundant — the short form should be the canonical way to invoke it.

Actual Behavior

The Skill tool requires the fully-qualified plugin:skill name even when they're identical, forcing the stutter-y refine-issue:refine-issue invocation.