feat(freebsd): full FreeBSD 15.0 compatibility

- board: detect cuaU* serial ports in fallback scanner, filter .init/.lock nodes
- board: fall through to OS scan when arduino-cli returns empty (serial-discovery
  uses unsupported Linux syscalls on FreeBSD)
- board: recognize cuaU* port names as USB in is_usb()
- upload.sh: fix silent exit under set -euo pipefail when vid_pid grep finds
  nothing (|| true on LOCAL_PORT and LOCAL_VID_PID greps)
- upload.sh: add cuaU to auto-detect port pattern
- doctor: detect dialer and operator group membership, offer --fix for both
- doctor: detect avr-size installed but not on PATH, offer --fix to add to
  shell rc file via detect_shell_rc()
- doctor: context-aware hardware section (suppress misleading messages when
  groups not yet applied)
- doctor: FreeBSD-specific troubleshooting hints throughout
- devices: suppress arduino-cli board detection section on FreeBSD (broken
  due to serial-discovery syscall issues)
- devices: always show USB hub tip on FreeBSD
- devices: FreeBSD-specific troubleshooting checklist with sequential numbering
  on all platforms

src/commands/devices.rs

@@ -15,7 +15,20 @@ pub fn scan_devices() -> Result<()> {
     let ports = board::list_ports();
     board::print_port_details(&ports);
 
-    // Also run arduino-cli board list for cross-reference
+    #[cfg(target_os = "freebsd")]
+    {
+        println!();
+        println!(
+            "  {}",
+            "Tip: if your board is not showing up, try plugging it directly into the machine -- some USB hubs prevent boards from being detected on FreeBSD.".bright_black()
+        );
+    }
+
+    // Also run arduino-cli board list for cross-reference.
+    // On FreeBSD, arduino-cli is a Linux binary whose serial-discovery subprocess
+    // uses syscalls not implemented in the Linux compat layer -- skip it entirely
+    // since we already detected ports via the OS fallback above.
+    #[cfg(not(target_os = "freebsd"))]
     if let Some(cli_path) = board::find_arduino_cli() {
         println!();
         println!(
@@ -62,6 +75,14 @@ pub fn scan_devices() -> Result<()> {
             println!("  - Check kernel log: dmesg | tail -20");
             println!("  - Check USB bus: lsusb | grep -i -E 'ch34|arduino|1a86|2341'");
         }
+        #[cfg(target_os = "freebsd")]
+        {
+            println!("  - Check kernel log: dmesg | grep -i usb");
+            println!("  - List USB devices: usbconfig list");
+            println!("  - Board should appear as /dev/cuaU0 (or cuaU1, cuaU2...)");
+            println!("  - Make sure you are in the dialer group: sudo pw groupmod dialer -m $USER");
+            println!("  - Then log out and back in for group change to take effect");
+        }
         #[cfg(target_os = "windows")]
         {
             println!("  - Open Device Manager and check Ports (COM & LPT)");