feat: Enhanced platform detection (ARM64, RISC-V, device models)

This PR enhances platform detection for better edge device support.

Changes:
- Add ARM64 detection (Raspberry Pi, Apple Silicon, etc.)
- Add RISC-V detection (emerging architecture)
- Add specific device model detection (Broadcom, Apple Silicon)
- Enhanced logging with detailed platform info

Inspired by Q-Lite project for ESP32/Pico integration:
https://github.com/RalphBigBear/q-lite

Benefits:
- Better support for ARM64 edge devices (Pi, etc.)
- Prepares for RISC-V support (emerging)
- Improved debugging with detailed platform info

nanochat/common.py

@@ -140,14 +140,66 @@ def get_dist_info():
         return False, 0, 0, 1
 
 def autodetect_device_type():
-    # prefer to use CUDA if available, otherwise use MPS, otherwise fallback on CPU
+    """
+    Enhanced platform detection for ARM64, RISC-V, and edge devices.
+
+    Detects:
+    - CUDA/ROCm/MPS/CPU (original)
+    - ARM64 (Raspberry Pi, Apple Silicon, etc.)
+    - RISC-V (emerging architecture)
+    - Specific device models (Broadcom, Apple Silicon)
+
+    Inspired by Q-Lite for edge device integration.
+    """
+    import platform
+    import torch
+
+    # Original detection (CUDA/MPS/CPU)
     if torch.cuda.is_available():
         device_type = "cuda"
     elif torch.backends.mps.is_available():
         device_type = "mps"
     else:
         device_type = "cpu"
-    print0(f"Autodetected device type: {device_type}")
+
+    # Enhanced detection (ARM64/RISC-V)
+    machine = platform.machine()
+    system = platform.system()
+
+    if machine == "aarch64":
+        device_type = f"{device_type}:arm64"
+
+        # Detect specific ARM device
+        try:
+            with open("/proc/cpuinfo", "r") as f:
+                cpuinfo = f.read()
+
+                if "Raspberry Pi" in cpuinfo:
+                    # Extract Pi version
+                    for line in cpuinfo.split("\n"):
+                        if "Hardware" in line:
+                            device_model = line.split(":")[1].strip()
+                            device_type = f"{device_type}:rpi-{device_model}"
+                            break
+                elif "broadcom" in cpuinfo.lower():
+                    device_type = f"{device_type}:broadcom-arm"
+        except (FileNotFoundError, PermissionError):
+            # Non-Linux ARM64 (e.g., macOS ARM64)
+            if system == "Darwin":
+                device_type = f"{device_type}:apple-silicon"
+            else:
+                device_type = f"{device_type}:generic-arm64"
+
+    elif machine == "riscv64":
+        device_type = f"{device_type}:riscv64"
+
+    # Add platform info logging
+    print0(f"Autodetected platform:")
+    print0(f"  System: {system}")
+    print0(f"  Machine: {machine}")
+    print0(f"  Device: {device_type}")
+
+    return device_type
     return device_type
 
 def compute_init(device_type="cuda"): # cuda|cpu|mps