feat: Add USB and direct-attach device detection

[iamh2o]

Summary

Implements automatic discovery of locally connected devices (USB and direct-attach) on the local machine.

Changes

New CLI Command: marvain devices detect

# Detect all devices
marvain devices detect

# Filter by device type
marvain devices detect --type video
marvain devices detect --type audio_input
marvain devices detect --type audio_output
marvain devices detect --type serial

# Filter by connection type
marvain devices detect --connection usb
marvain devices detect --connection direct

# JSON output
marvain devices detect --format json

Device Detection

• Video devices: Cameras, webcams (AVFoundation on macOS, /dev/video* on Linux)
• Audio input: Microphones (CoreAudio on macOS)
• Audio output: Speakers (CoreAudio on macOS)
• Serial ports: USB-to-serial adapters (/dev/tty., /dev/cu.)

Implementation

• DetectedDevice dataclass in marvain_cli/ops.py
• detect_local_devices() aggregates all detection methods
• list_detected_devices() provides filtering and dict output
• Platform-specific detection using macOS APIs (AVFoundation, CoreAudio)

Tests

• 8 new tests in tests/test_ops.py::TestDeviceDetection
• All tests passing

Testing

# Run device detection tests
python -m pytest tests/test_ops.py::TestDeviceDetection -v

# Manual test
marvain devices detect

Files Changed

• marvain_cli/ops.py: Device detection functions
• marvain_cli/typer_app.py: devices detect command
• marvain_cli/argparse_app.py: devices detect command (fallback)
• tests/test_ops.py: 8 new tests

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Pull Request opened by Augment Code with guidance from the PR author

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use a real USB check for Linux video devices

On Linux, conn_type is set to "usb" whenever /sys/class/video4linux/<device>/device/driver exists. That path exists for essentially every v4l2 device (PCI, platform, virtual, etc.), so non‑USB cameras will still be marked as USB. In practice this makes --connection direct return no results even when direct‑attach devices are present, and mislabels devices in the output. Consider checking the sysfs device ancestry for a USB bus (e.g., via /sys/class/video4linux/<device>/device/subsystem or udevadm) instead of only the driver path.

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