boards/lckfb-szpi-esp32s3: add vncviewer defconfig and documentation

Add vncviewer board configuration and documentation:
- boards: add lckfb-szpi-esp32s3:vncviewer defconfig
- Documentation: add system/vncviewer application doc with host
  VNC server setup examples (Xvfb, clip, scale modes) and images

Assisted-by: GitHubCopilot:claude-4.6-opus
Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

Documentation/applications/system/vncviewer/index.rst

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+===========================
+``vncviewer`` VNC Viewer
+===========================
+
+A lightweight VNC viewer that renders a remote desktop on an LCD display via
+the NuttX LCD character device interface (``/dev/lcd0``).
+
+Features:
+
+- RFB 3.8 protocol with VNC Authentication (pure software DES, no external library)
+- Auto-detect pixel format from LCD driver
+- Raw encoding with row-by-row rendering — minimal RAM usage
+- Automatic reconnection on disconnect
+
+Prepare
+==========================
+
+- Enable the VNC Viewer application (Device):
+
+  .. code-block:: bash
+
+     CONFIG_NET_TCP=y
+     CONFIG_LCD=y
+     CONFIG_SYSTEM_VNCVIEWER=y
+
+- Ensure the device has a working LCD driver (``/dev/lcd0``) and TCP/IP network connectivity.
+
+- Install a VNC server on the host. For example, on Ubuntu:
+
+  .. code-block:: bash
+
+     sudo apt install x11vnc xvfb openbox xterm
+
+Usage
+==========================
+
+.. code-block:: bash
+
+   vncviewer [options] <host> [port]
+
+Options:
+
+- ``-p <password>`` — VNC password
+- ``-d <devno>`` — LCD device number (default: 0)
+- ``-h`` — Show help
+
+Default port: 5900
+
+Host VNC Server Configuration
+==============================
+
+Three server modes are supported:
+
+1. Xvfb Virtual Desktop (Pixel-Perfect 1:1)
+---------------------------------------------
+
+Create a virtual framebuffer matching the LCD resolution (e.g., 320×240):
+
+.. code-block:: bash
+
+   # Start virtual display
+   Xvfb :1 -screen 0 320x240x16 &
+   DISPLAY=:1 openbox &
+   DISPLAY=:1 xterm -geometry 38x11+0+0 -fa Monospace -fs 10 &
+
+   # Start VNC server
+   x11vnc -display :1 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg
+
+On the device:
+
+.. code-block:: bash
+
+   vncviewer -p mypasswd <host_ip> 5901
+
+.. figure:: vncviewer_xvfb.png
+   :align: center
+
+   Xvfb virtual desktop — host side (320×240 xterm in VNC viewer)
+
+.. figure:: vncviewer_xvfb_lcd.jpg
+   :align: center
+
+   Xvfb virtual desktop — device side (rendered on ST7789 LCD)
+
+2. Physical Desktop Clip (Top-Left Region)
+-------------------------------------------
+
+Clip a region of the physical desktop matching the LCD resolution:
+
+.. code-block:: bash
+
+   x11vnc -display :0 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg -clip 320x240+0+0
+
+On the device:
+
+.. code-block:: bash
+
+   vncviewer -p mypasswd <host_ip> 5901
+
+3. Physical Desktop Scaled
+-------------------------------------------
+
+Scale the full desktop down to the LCD resolution:
+
+.. code-block:: bash
+
+   x11vnc -display :0 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg -scale 320x240
+
+On the device:
+
+.. code-block:: bash
+
+   vncviewer -p mypasswd <host_ip> 5901
+
+Examples
+==========================
+
+Connect to a VNC server with password:
+
+.. code-block:: bash
+
+   vncviewer -p mypasswd 192.168.1.100 5901
+
+Connect using a different LCD device:
+
+.. code-block:: bash
+
+   vncviewer -d 1 -p mypasswd 192.168.1.100 5900

boards/xtensa/esp32s3/lckfb-szpi-esp32s3/configs/vncviewer/defconfig

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+#
+# This file is autogenerated: PLEASE DO NOT EDIT IT.
+#
+# You can use "make menuconfig" to make any modifications to the installed .config file.
+# You can then do "make savedefconfig" to generate a new defconfig file that includes your
+# modifications.
+#
+# CONFIG_ARCH_LEDS is not set
+# CONFIG_NSH_ARGCAT is not set
+# CONFIG_NSH_CMDOPT_HEXDUMP is not set
+CONFIG_ALLOW_BSD_COMPONENTS=y
+CONFIG_ARCH="xtensa"
+CONFIG_ARCH_BOARD="lckfb-szpi-esp32s3"
+CONFIG_ARCH_BOARD_COMMON=y
+CONFIG_ARCH_BOARD_ESP32S3_LCKFB_SZPI=y
+CONFIG_ARCH_CHIP="esp32s3"
+CONFIG_ARCH_CHIP_ESP32S3=y
+CONFIG_ARCH_CHIP_ESP32S3WROOM1N16R8=y
+CONFIG_ARCH_INTERRUPTSTACK=2048
+CONFIG_ARCH_IRQ_TO_NDX=y
+CONFIG_ARCH_MINIMAL_VECTORTABLE_DYNAMIC=y
+CONFIG_ARCH_NUSER_INTERRUPTS=2
+CONFIG_ARCH_STACKDUMP=y
+CONFIG_ARCH_XTENSA=y
+CONFIG_BOARD_LOOPSPERMSEC=16717
+CONFIG_BUILTIN=y
+CONFIG_DEBUG_FEATURES=y
+CONFIG_DEBUG_FULLOPT=y
+CONFIG_DEBUG_SYMBOLS=y
+CONFIG_DEV_GPIO=y
+CONFIG_DRIVERS_IEEE80211=y
+CONFIG_DRIVERS_VIDEO=y
+CONFIG_DRIVERS_WIRELESS=y
+CONFIG_ESP32S3_GPIO_IRQ=y
+CONFIG_ESP32S3_I2C0=y
+CONFIG_ESP32S3_SPI2=y
+CONFIG_ESP32S3_SPI2_CLKPIN=41
+CONFIG_ESP32S3_SPI2_CSPIN=-1
+CONFIG_ESP32S3_SPI2_MISOPIN=-1
+CONFIG_ESP32S3_SPI2_MOSIPIN=40
+CONFIG_ESP32S3_SPIFLASH=y
+CONFIG_ESP32S3_SPIFLASH_SPIFFS=y
+CONFIG_ESP32S3_SPI_SWCS=y
+CONFIG_ESP32S3_SPI_UDCS=y
+CONFIG_ESP32S3_UART0=y
+CONFIG_ESPRESSIF_LEDC=y
+CONFIG_ESPRESSIF_LEDC_CHANNEL0_PIN=42
+CONFIG_ESPRESSIF_LEDC_TIMER0=y
+CONFIG_ESPRESSIF_WIFI=y
+CONFIG_FS_PROCFS=y
+CONFIG_GPIO_LOWER_HALF=y
+CONFIG_HAVE_CXX=y
+CONFIG_HAVE_CXXINITIALIZE=y
+CONFIG_IDLETHREAD_STACKSIZE=3072
+CONFIG_INIT_ENTRYPOINT="nsh_main"
+CONFIG_INIT_STACKSIZE=3072
+CONFIG_INTELHEX_BINARY=y
+CONFIG_IOB_BUFSIZE=400
+CONFIG_IOB_NBUFFERS=100
+CONFIG_IOB_NCHAINS=32
+CONFIG_IOB_THROTTLE=40
+CONFIG_IOEXPANDER=y
+CONFIG_IOEXPANDER_NPINS=8
+CONFIG_IOEXPANDER_PCA9557=y
+CONFIG_LCD=y
+CONFIG_LCD_DEV=y
+CONFIG_LCD_FRAMEBUFFER=y
+CONFIG_LCD_ST7789=y
+CONFIG_LCD_ST7789_DATA_ENDIAN_LITTLE=y
+CONFIG_LCD_ST7789_FREQUENCY=40000000
+CONFIG_LINE_MAX=64
+CONFIG_NETDB_DNSCLIENT=y
+CONFIG_NETDEV_LATEINIT=y
+CONFIG_NETDEV_PHY_IOCTL=y
+CONFIG_NETDEV_WIRELESS_IOCTL=y
+CONFIG_NET_ETH_PKTSIZE=1514
+CONFIG_NET_ICMP_SOCKET=y
+CONFIG_NET_TCP=y
+CONFIG_NET_TCP_DELAYED_ACK=y
+CONFIG_NET_TCP_WRITE_BUFFERS=y
+CONFIG_NET_UDP=y
+CONFIG_NET_UDP_WRITE_BUFFERS=y
+CONFIG_NSH_ARCHINIT=y
+CONFIG_NSH_BUILTIN_APPS=y
+CONFIG_NSH_FILEIOSIZE=512
+CONFIG_NSH_READLINE=y
+CONFIG_PREALLOC_TIMERS=4
+CONFIG_PTHREAD_MUTEX_TYPES=y
+CONFIG_RAM_SIZE=114688
+CONFIG_RAM_START=0x20000000
+CONFIG_RR_INTERVAL=200
+CONFIG_SCHED_LPWORK=y
+CONFIG_SCHED_WAITPID=y
+CONFIG_SPI_CMDDATA=y
+CONFIG_START_DAY=6
+CONFIG_START_MONTH=12
+CONFIG_START_YEAR=2011
+CONFIG_SYSLOG_BUFFER=y
+CONFIG_SYSTEM_DHCPC_RENEW=y
+CONFIG_SYSTEM_NSH=y
+CONFIG_SYSTEM_PING=y
+CONFIG_SYSTEM_VNCVIEWER=y
+CONFIG_TIMER=y
+CONFIG_TLS_TASK_NELEM=4
+CONFIG_UART0_SERIAL_CONSOLE=y
+CONFIG_VIDEO=y
+CONFIG_VIDEO_FB=y
+CONFIG_WIRELESS=y
+CONFIG_WIRELESS_WAPI=y
+CONFIG_WIRELESS_WAPI_CMDTOOL=y
+CONFIG_WIRELESS_WAPI_STACKSIZE=4096