chore: bump version to 1.7.1+15

The channel sidebar is an incremental change on top of v1.7.0, so ship it
as a patch release instead of 1.8.0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L8c4kaH8AXVT5UUie3zR4p

pubspec.yaml

@@ -1,7 +1,7 @@
 name: xtremobile
 description: High-performance IPTV Android Application with Xtream Codes API
 publish_to: 'none'
-version: 1.8.0+15
+version: 1.7.1+15
 
 environment:
   sdk: '>=3.0.0 <4.0.0'