Window: remove ellipses from button labels

[emaspa]

Changes

• Shorten the mix-master mute button label to Mute.
• Remove ellipses from button labels across the UI, including dynamic Inserts labels.
• Update the manual and feature documentation to match.
• Keep progress messages, placeholder prompts and text-truncation indicators unchanged.
• Add regression checks for literal XAML button labels and dynamic insert labels.

Verification

• Native-enabled Release build passed with 0 warnings and 0 errors.
• Combined .NET suite: 510 passed, 3 opt-in desktop tests skipped.
• Separate Xvfb layout checks passed; inspected the generated controls and confirmed the new labels fit.
• Local UI relaunched and verified without restarting audio.

No version bump or release changes. Editor compatibility policy is a separate PR.