fix(dashboard-api): wire Apple Silicon into /api/gpu/detailed

[yasinBursali]

What

Wire Apple Silicon GPU detection into /api/gpu/detailed so the endpoint returns real data instead of a 503 on macOS.

Why

_get_raw_gpus in routers/gpu.py only had a branch for amd, then fell through to NVIDIA/AMD sysfs probing — both return None on macOS, yielding an empty list. The existing get_gpu_info_apple() call (already used by /api/features) was never consulted, so every call to /api/gpu/detailed on Apple Silicon returned 503 No GPU data available.

How

• routers/gpu.py: import get_gpu_info_apple alphabetically into the existing from gpu import (...) block; add private helper _apple_info_to_individual(info: GPUInfo) -> IndividualGPU that wraps the aggregate GPUInfo into a single IndividualGPU with index=0 and uuid="apple-unified-0" (≥8 chars, satisfies GPUCard.jsx .slice(-8) key requirement); add "apple" as the first branch in _get_raw_gpus, returning [_apple_info_to_individual(info)] or None if detection fails (propagates to the existing 503 path).
• tests/test_gpu_detailed.py: new fixture _sample_apple_gpu_info(); 3 new tests covering single-entry return, None-propagation, and full endpoint 200 response with Apple aggregate data.

Testing

• Automated: pytest tests/test_gpu_detailed.py -k "not history" — 19/19 pass; ruff clean.
• Manual: On Apple Silicon Mac, curl -H "Authorization: Bearer $DASHBOARD_API_KEY" http://localhost:$DASHBOARD_API_PORT/api/gpu/detailed should return HTTP 200 with a single-entry gpus array (chip name, VRAM, utilization 0, temperature 0, power_w null).

Known Considerations

• Apple GPU utilization and temperature are hard-zero in this implementation — IOKit metrics are not accessible from Python in this context. A future PR could expose them via powermetrics or direct IOKit bindings. Out of scope here.
• power_w is None on Apple; the dashboard already handles this gracefully.

Platform Impact

• macOS (Apple Silicon): Fixed — /api/gpu/detailed now returns 200 with GPU data.
• Linux (NVIDIA/AMD): Not affected — new branch is gated on exact string "apple"; existing NVIDIA/AMD paths unchanged.
• Windows (WSL2): Not affected — same as Linux; Apple branch never executes.