fix: Install wshowlyrics-offset helper script to /usr/bin

Add explicit installation of wshowlyrics-offset script that provides runtime
control for adjusting lyrics offset. This script was already included in
meson.build but was missing from manual installation in wshowlyrics-git PKGBUILD.

Changes:
- Add install command for wshowlyrics-offset with executable permissions
- Use Dm755 mode (drwx r-x r-x with file rwx r-- r--)
- Position after binary installation with descriptive comment

Benefits:
- Users can now adjust lyrics timing offset at runtime
- Consistent with stable package behavior
- Matches meson.build configuration

Fixes: Missing utility script in git package

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

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

PKGBUILD

@@ -54,6 +54,9 @@ package() {
     # Install binary
     install -Dm755 build/lyrics "$pkgdir/usr/bin/wshowlyrics"
 
+    # Install helper script for runtime offset control
+    install -Dm755 wshowlyrics-offset "$pkgdir/usr/bin/wshowlyrics-offset"
+
     # Install system-wide configuration file
     install -Dm644 settings.ini.example "$pkgdir/etc/wshowlyrics/settings.ini"