fix(skill): resolve namespaced skills by short name

When a skill has a namespaced name like 'superpowers/systematic-debugging',
users see the short name 'systematic-debugging' in the listing but can't
invoke it — the resolver only accepts exact full names.

Add short-name fallback: if exact match fails, try matching the basename
of namespaced skills. Only resolves when unambiguous (single match).

- Exact match still takes priority
- Ambiguous short names (multiple namespaces) fall through to error
- 4 new tests covering all cases

Fixes #2971

src/tools/skill/tools.ts

@@ -324,7 +324,19 @@ export function createSkillTool(options: SkillLoadOptions = {}): ToolDefinition
       const requestedName = args.name.replace(/^\//, "")
 
       // Check skills first (exact match, case-insensitive)
-      const matchedSkill = skills.find(s => s.name.toLowerCase() === requestedName.toLowerCase())
+      let matchedSkill = skills.find(s => s.name.toLowerCase() === requestedName.toLowerCase())
+
+      // Fallback: try matching by short name (basename) for namespaced skills
+      // e.g. "systematic-debugging" matches "superpowers/systematic-debugging"
+      if (!matchedSkill) {
+        const shortNameMatches = skills.filter(s => {
+          const parts = s.name.split("/")
+          return parts.length > 1 && parts[parts.length - 1].toLowerCase() === requestedName.toLowerCase()
+        })
+        if (shortNameMatches.length === 1) {
+          matchedSkill = shortNameMatches[0]
+        }
+      }
 
       if (matchedSkill) {
         if (matchedSkill.definition.agent && (!ctx?.agent || matchedSkill.definition.agent !== ctx.agent)) {