Update default branch from main to 4.1 in Pi docs

Branch 4.1 includes Reed-Solomon error correction for DCT
steganography which is required for reliable operation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

rpi/stegasoo.conf.example

@@ -14,8 +14,8 @@
 # Git repository URL
 #STEGASOO_REPO="https://github.com/adlee-was-taken/stegasoo.git"
 
-# Git branch to checkout (default: main)
-#STEGASOO_BRANCH="main"
+# Git branch to checkout (default: 4.1)
+#STEGASOO_BRANCH="4.1"
 
 # Web UI port (default: 5000)
 #STEGASOO_PORT="5000"