Add focused app volume hotkeys

[Alb11747]

Summary

Add configurable shortcuts to raise, lower, or toggle mute for the focused app, and expose them in EarTrumpet's shortcut settings. Share foreground-app resolution with the Actions add-on.

Focused-app resolution

• Resolve regular Win32 and hosted ApplicationFrameWindow apps.
• Inspect the full audio-session hierarchy using each stream's process ID and activity state. Target an active descendant app only when exactly one distinct descendant owns an active session, covering injected overlays.
• Fall back to the actual foreground app when the target is missing or ambiguous.
• Validate process ancestry with creation times so reused parent IDs cannot redirect controls to unrelated apps.

Volume behavior

• Apply fixed steps of 2 percentage points in linear mode and 0.5 dB in logarithmic mode to individual streams across matching groups and devices. For example, volume-down changes 50% and 10% to 48% and 8%.
• Mute every matching stream when any is unmuted; unmute only when all are muted.
• Preserve clamping, non-finite recovery, and temporary entries used during device moves.
• Keep logarithmic readback consistent with the scalar sent to Core Audio, so repeated shortcuts work before callbacks arrive.

Validation

• 17 deterministic regression tests pass, covering nested groups, unequal volumes, mute states, boundaries, placeholders, ancestry, PID reuse, and immediate logarithmic readback. The runner is included in PR CI.
• Release and VSDebug builds pass for x64, x86, and ARM64. Existing x86 interop warnings remain.
• An isolated live Core Audio session passed repeated linear/logarithmic adjustments and mute/unmute through the production helper, view model, and audio session.
• Debug builds remain blocked by pre-existing audio mocks missing volume-interface methods, reproduced at the original PR head.
• Full shortcut registration, Actions targeting, multiple live audio devices, and ARM64 runtime execution remain unverified.

Scope

Toast notifications and configurable volume-step sizes remain on the separate local toast branch. This PR keeps fixed step sizes and adds no toast UI.

[CLAassistant]

All committers have signed the CLA.

[Loukious]

You may want to add a mute/unmute foreground app while at it. I think that would be the most important feature for gamers.