feat: Add v0.3 OTA updates — dual partition, esp-ota tool, rollback

Dual OTA partition table (ota_0/ota_1, 1920 KB each) on 4MB flash.
Firmware gains OTA command, LED_OTA double-blink, version in STATUS,
and automatic rollback validation. Pi-side esp-ota tool serves firmware
via HTTP and orchestrates the update flow. esp-fleet gains ota subcommand.

tools/esp-ota

@@ -0,0 +1,149 @@
+#!/usr/bin/env python3
+"""OTA firmware update for ESP32 CSI devices."""
+
+import argparse
+import http.server
+import os
+import socket
+import sys
+import threading
+import time
+
+DEFAULT_CMD_PORT = 5501
+DEFAULT_HTTP_PORT = 8070
+DEFAULT_FW = os.path.expanduser(
+    "~/git/esp32-hacking/get-started/csi_recv_router/build/csi_recv_router.bin"
+)
+TIMEOUT = 2.0
+REBOOT_WAIT = 25.0
+STATUS_RETRIES = 10
+STATUS_INTERVAL = 3.0
+
+
+def resolve(host: str) -> str:
+    """Resolve hostname to IP address."""
+    try:
+        result = socket.getaddrinfo(host, DEFAULT_CMD_PORT, socket.AF_INET, socket.SOCK_DGRAM)
+        return result[0][4][0]
+    except socket.gaierror as e:
+        print(f"ERR: cannot resolve {host}: {e}", file=sys.stderr)
+        sys.exit(1)
+
+
+def udp_cmd(ip: str, cmd: str, timeout: float = TIMEOUT) -> str:
+    """Send UDP command and return reply."""
+    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    sock.settimeout(timeout)
+    try:
+        sock.sendto(cmd.encode(), (ip, DEFAULT_CMD_PORT))
+        data, _ = sock.recvfrom(512)
+        return data.decode().strip()
+    finally:
+        sock.close()
+
+
+def get_local_ip(target_ip: str) -> str:
+    """Determine which local IP the target can reach us on."""
+    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    try:
+        sock.connect((target_ip, 80))
+        return sock.getsockname()[0]
+    finally:
+        sock.close()
+
+
+def serve_firmware(directory: str, port: int) -> http.server.HTTPServer:
+    """Start HTTP server serving firmware directory in a background thread."""
+    handler = lambda *a, **k: http.server.SimpleHTTPRequestHandler(
+        *a, directory=directory, **k
+    )
+    server = http.server.HTTPServer(("0.0.0.0", port), handler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    return server
+
+
+def main():
+    parser = argparse.ArgumentParser(description="OTA firmware update for ESP32 CSI devices")
+    parser.add_argument("host", help="Device hostname or IP (e.g., amber-maple.local)")
+    parser.add_argument("-f", "--firmware", default=DEFAULT_FW, help="Path to firmware .bin")
+    parser.add_argument("-p", "--port", type=int, default=DEFAULT_HTTP_PORT, help="HTTP server port")
+    parser.add_argument("--no-wait", action="store_true", help="Don't wait for reboot verification")
+    args = parser.parse_args()
+
+    fw_path = os.path.abspath(args.firmware)
+    if not os.path.isfile(fw_path):
+        print(f"ERR: firmware not found: {fw_path}", file=sys.stderr)
+        sys.exit(1)
+
+    fw_size = os.path.getsize(fw_path)
+    fw_dir = os.path.dirname(fw_path)
+    fw_name = os.path.basename(fw_path)
+
+    print(f"Firmware: {fw_path} ({fw_size // 1024} KB)")
+
+    # Resolve device
+    ip = resolve(args.host)
+    print(f"Device:   {args.host} ({ip})")
+
+    # Check device is alive
+    try:
+        reply = udp_cmd(ip, "STATUS")
+        print(f"Status:   {reply}")
+    except (socket.timeout, OSError) as e:
+        print(f"ERR: device not responding: {e}", file=sys.stderr)
+        sys.exit(1)
+
+    # Determine local IP
+    local_ip = get_local_ip(ip)
+    ota_url = f"http://{local_ip}:{args.port}/{fw_name}"
+    print(f"OTA URL:  {ota_url}")
+
+    # Start HTTP server
+    server = serve_firmware(fw_dir, args.port)
+    print(f"HTTP server on port {args.port}")
+
+    # Send OTA command
+    try:
+        reply = udp_cmd(ip, f"OTA {ota_url}")
+        print(f"OTA cmd:  {reply}")
+    except (socket.timeout, OSError) as e:
+        server.shutdown()
+        print(f"ERR: OTA command failed: {e}", file=sys.stderr)
+        sys.exit(1)
+
+    if not reply.startswith("OK"):
+        server.shutdown()
+        print(f"ERR: device rejected OTA: {reply}", file=sys.stderr)
+        sys.exit(1)
+
+    if args.no_wait:
+        print("OTA started (--no-wait, not verifying)")
+        # Keep server alive briefly for download
+        time.sleep(30)
+        server.shutdown()
+        return
+
+    # Wait for device to download, flash, and reboot
+    print(f"Waiting for reboot...")
+    time.sleep(REBOOT_WAIT)
+
+    # Verify device comes back
+    for attempt in range(1, STATUS_RETRIES + 1):
+        try:
+            ip = resolve(args.host)
+            reply = udp_cmd(ip, "STATUS", timeout=3.0)
+            print(f"Verified: {reply}")
+            server.shutdown()
+            return
+        except (socket.timeout, OSError):
+            print(f"  retry {attempt}/{STATUS_RETRIES}...")
+            time.sleep(STATUS_INTERVAL)
+
+    server.shutdown()
+    print("ERR: device did not come back after OTA", file=sys.stderr)
+    sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()