chore: set version to 0.1.0 for the first release

pubspec.yaml still carried flutter create's placeholder 1.0.0+1, which would
have had the APK reporting 1.0.0 while the release was tagged v0.1.0. Matches
the version the tag records.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pubspec.yaml

@@ -2,7 +2,7 @@ name: iperf3gui
 description: "A Flutter-based Android GUI wrapper for iperf3."
 publish_to: 'none'
 
-version: 1.0.0+1
+version: 0.1.0+1
 
 environment:
   sdk: ^3.13.1