Improve Core Rules and clarify latest/latest-lts

- Promote non-existent relations to Core Rules (rule #4) for visibility
- Clarify that latest and latest-lts are same when latest is LTS,
  diverge when STS is newer

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

release-notes/skills/dotnet-releases/SKILL.md

@@ -29,6 +29,7 @@ Fetch when your query matches. **Core Rules apply to all.**
 1. **Follow `_links["..."].href` exactly** — never construct URLs
 2. **Use `_embedded` data first** — answers most queries without extra fetches
 3. **Don't fabricate** — report gaps
+4. **Non-existent relations:** `next` (use `prev`), `latest_sts` (use `latest`)
 
 ## llms.json Contents
 
@@ -59,8 +60,6 @@ From `llms.json._links`:
 
 | Relation | Target |
 | -------- | ------ |
-| `latest`, `latest-lts` | Newest release |
+| `latest`, `latest-lts` | Newest release (same when latest is LTS; diverge when STS is newer) |
 | `latest-security-month` | Current security month |
 | `releases-index` | All versions including EOL |
-
-**Non-existent relations:** `next` (use `prev`), `latest_sts` (use `latest`)