feat(FN-1513): track excluded skill paths and improve skill resolver diagnostics

- Add excludedSkillPaths to SkillSelectionResult to track skills disabled by - patterns
- Update createSkillsOverrideFromSelection to filter out excluded skills
- Produce warning diagnostics for disabled skills that exist but were excluded
- Add tests for excluded paths tracking and deterministic output order
- Update memory documentation with skill resolver diagnostics distinction
- Fix pi-create-kb-agent test to include excludedSkillPaths in selection mock

packages/engine/src/pi-create-kb-agent.test.ts

@@ -788,6 +788,7 @@ describe("createKbAgent", () => {
 
       const selection = {
         allowedSkillPaths: new Set(["/path/nonexistent"]),
+        excludedSkillPaths: new Set<string>(),
         diagnostics: [],
         filterActive: true,
       };