feat: standalone ReleaseUpdater library v1.1.0

Promoted from DIYStickyNotes/lib/ReleaseUpdater (byte-identical src) into a
reusable Gitea library. Adds LICENSE, .gitignore, library.properties,
keywords.txt and carries the ReleaseUpdaterCore native unit test for
downstream reuse.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,4 @@
+.pio/
+.vscode/
+*.o
+*.d