fix(skill-author): resolve skill-audit findings

- script: new-skill.sh now exits 0 when target already exists (idempotent
  retry-safe) instead of exit 1; --help updated to reflect narrowed error cases
- test: updated bats test to assert success and "nothing to do" output
- body: removed speculative "Extract the skill from a real task" advice
  (human-targeted, not agent-actionable)
- formatting: converted H4 headings in Step 2 to bold text (H2/H3 two-tier model)
- provenance: removed orphan agentskills-llms-txt entry from references/sources.md;
  added discovery-only comment

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/kyberforge/skills/skill-author/references/sources.md

@@ -1,5 +1,7 @@
 # Sources
 
+<!-- agentskills.io/llms.txt was used for initial source discovery and is not listed below; it contributed no skill file content directly. -->
+
 ## agentskills-home
 
 - **URL:** https://agentskills.io/home.md
@@ -49,9 +51,3 @@
 - **Contributing files:** SKILL.md
 - **Status:** `extracted`
 
-## agentskills-llms-txt
-
-- **URL:** https://agentskills.io/llms.txt
-- **Description:** Documentation index used for source discovery — lists all available pages with URLs
-- **Contributing files:** (none — used for discovery only)
-- **Status:** `extracted`