Add softer sound feedback on key release

[quanhavn]

Keyboard profiles currently play only on key-down because none of the bundled banks has dedicated release recordings. This adds a separate, softer return sound when the matching key is released across all ten profiles.

Return samples are prepared once at bank load: 1.2× speed, a maximum duration of 45 ms, and a tapered envelope at 45% amplitude. They inherit press normalization to preserve the softer level and use the existing release tracker, including modifier policy and reset handling. Dedicated release recordings keep their existing behavior. Runtime diagnostics and asset documentation describe the new behavior.

Validation:

• All 32 ClickyCore tests pass, including duration, level and clean-edge checks for all 60 derived variants.
• Release compilation and ad-hoc bundle signature verification pass. Persistent local signing is not configured on this machine.
• Real-engine replay: 60 down/up pairs produce 120 accepted triggers in each of ten profiles, with zero drops. Modifier replay and the 500-trigger stress check pass.
• Recorded asset checks pass for all 60 recordings and five effects; generated Xcode project remains unchanged.