Window: compact the applications card

[emaspa]

Changes

• Move Manage beside the Applications heading, matching Edit layout in the Submixer heading.
• Remove the redundant explanatory text below the apps.
• Reduce horizontal gaps from 8 to 4 pixels without changing dropdown sizes, so the reported six-app set fits on one row at full card width.
• Keep the mixer content stretched within its existing width cap, so wrapped app rows cannot shrink the entire page.
• Update the manual and layout regression tests.

Verification

• Native-enabled Release build with warnings treated as errors: 0 warnings, 0 errors.
• .NET suite: 487 passed, 3 opt-in desktop tests skipped.
• Separate Xvfb layout checks passed at 100% and 175% scaling, across window widths from 640 to 2400 pixels. The six-app fixture covers Google Chrome, Discord, Karere, Signal, Steam and Balatro with their actual routing labels.
• Inspected rendered layouts and confirmed the local UI works. No audio-service restart or routing changes were needed.

No version bump or release changes.