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>

keywords.txt

@@ -0,0 +1,14 @@
+ReleaseUpdater	KEYWORD1
+ReleaseUpdaterService	KEYWORD1
+RuConfig	KEYWORD1
+RuVersion	KEYWORD1
+RuRelease	KEYWORD1
+RuState	KEYWORD1
+check	KEYWORD2
+downloadAndFlash	KEYWORD2
+isNewer	KEYWORD2
+begin	KEYWORD2
+pendingReboot	KEYWORD2
+ruVersionParse	KEYWORD2
+ruVersionCompare	KEYWORD2
+ruParseLatestRelease	KEYWORD2