Add device subdirectory support for APPS layout in firmware

[jLynx]

Summary

This PR optimizes the release workflow by consolidating device-specific SD card assets into a single "universal" ZIP file. It also introduces a structured directory layout for external applications (.ppma/.ppmp), ensuring that different hardware targets (HackRF, PortaRF, HackRF Pro) load the correct binaries from dedicated subdirectories on the SD card.

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Key Changes

1. Workflow & Release Optimization

• Asset Consolidation: Replaced the generation of 6 individual SD card ZIPs (3 devices × 2 map variants) with 2 consolidated ZIPs (Standard and No-World-Map).
• Multi-Device Bundle: The CI now unzips and merges the artifacts for HackRF, PortaRF, and HackRF Pro into a single distribution, reducing clutter in the GitHub Releases page.
• Matrix Enhancements: Added device_subdir to the build matrix to facilitate organized file placement during the build process.

2. Firmware & App Directory Logic

• Namespaced Apps: External applications are now stored in APPS/<device_subdir>/ (e.g., APPS/hackrf, APPS/portarf, or APPS/hpro) instead of a flat APPS/ root.
• Dynamic Path Resolution:
  • Added init_apps_dir() in file_path.cpp to detect the hardware at runtime and point the apps_dir path to the correct subdirectory.
  • Modified main.cpp to initialize these paths immediately after successful hardware initialization.
• Build System Updates: CMakeLists.txt and internal helper scripts (copy_external_apps.sh, fast_flash_pp_and_copy_apps.py) now respect the DEVICE_SUBDIR environment variable.

3. Build System Improvements

• Unified OCI/PPFW: Firmware naming now includes the artifact_suffix consistently across nightly and stable workflows to prevent binary collisions when creating combined archives.

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Technical Details

Feature	Old Behavior	New Behavior
SD Card Layout	/APPS/*.ppma	/APPS/<device>/*.ppma
Release Assets	6 separate ZIP files for SD cards	2 "All-in-one" ZIP files
App Loading	Hardcoded to /APPS	Runtime detection based on portapack::device_type
CI Complexity	Uploaded multiple redundant artifacts	Merges device artifacts into a single combined release

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Impact

• Users: Can now use a single "Copy to SD Card" ZIP that works across all supported Mayhem hardware variants.
• Developers: Cleaner release page and more robust handling of device-specific binary requirements.

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Important

Ensure that existing users are informed to move their custom apps to the new subdirectories or perform a clean install from the new consolidated SD card ZIP to ensure apps remain visible in the UI.