Fix macOS 15 (Sequoia) build: update embedded JUCE

Building ysfx on macOS 15 / Xcode 16 fails during juceaide with:

'CGWindowListCreateImage' is unavailable: obsoleted in macOS 15.0 - Please use ScreenCaptureKit instead.

This happens because JUCE 7.0.0 still references APIs removed in the macOS 15 SDK. Newer JUCE releases use ScreenCaptureKit and compile cleanly.

What this PR changes

• Update JUCE to 8.0.10 via FetchContent so juceaide builds against the macOS 15 SDK.
• Switch to FetchContent_MakeAvailable (modern CMake) and set DOWNLOAD_EXTRACT_TIMESTAMP TRUE to silence CMake policy warnings.

Rationale

• macOS 15 SDK obsoletes CGWindowListCreateImage; older JUCE fails to compile.
• JUCE 8.x includes the replacement using ScreenCaptureKit, resolving the error.

###Notes / Impact

• No code changes to ysfx itself—only the embedded JUCE version and FetchContent usage.
• Linux/Windows builds unaffected.
• macOS ≤14 continues to build as before.

Build verification

• ✅ Configures and builds on macOS 15 (Sequoia) with Xcode 16 / AppleClang 17.
• ✅ juceaide “Testing/Finished setting up” completes, then project builds successfully.

Maintenance

• Keeps CMake warnings at bay (CMP0135/CMP0169).
• Future JUCE updates remain a one-liner in the FetchContent_Declare.

If you prefer a different JUCE tag (e.g., a specific 8.x point release), I’m happy to update this PR. Thanks!