Documentation: Add getevent input event monitor documentation.

Documentation/applications/graphics/input/getevent.rst

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+================================
+``getevent`` Input Event Monitor
+================================
+
+``getevent`` is a command-line input event monitor. It captures and displays
+real-time events from mouse, touchscreen, and keyboard devices via the input
+subsystem.
+
+It is useful for driver bring-up, input debugging, and system integration
+testing.
+
+Supported Event Types
+=====================
+
+- **Mouse** -- button state, x/y coordinates, wheel (when
+  ``CONFIG_INPUT_MOUSE_WHEEL`` is enabled)
+- **Touchscreen** -- multi-touch points with coordinates, flags, timestamps,
+  and optional pressure/size detail
+- **Keyboard** -- key code and event type
+
+Configuration
+=============
+
+Enable ``getevent`` in the NuttX configuration::
+
+  CONFIG_GRAPHICS_INPUT_GETEVENT=y
+
+Optional settings:
+
+.. list-table::
+   :header-rows: 1
+
+   * - Option
+     - Default
+     - Description
+   * - ``CONFIG_GRAPHICS_INPUT_GETEVENT_STACKSIZE``
+     - ``DEFAULT_TASK_STACKSIZE``
+     - Stack size for the getevent task
+   * - ``CONFIG_GRAPHICS_INPUT_GETEVENT_PRIORITY``
+     - ``100``
+     - Task priority
+   * - ``CONFIG_GRAPHICS_INPUT_GETEVENT_DETAIL_INFO``
+     - ``n``
+     - Show additional touch detail (pressure, width, height)
+
+Usage
+=====
+
+Auto-detect all input devices::
+
+  nsh> getevent
+
+Monitor specific devices::
+
+  nsh> getevent -m /dev/mouse0
+  nsh> getevent -t /dev/input0
+  nsh> getevent -k /dev/kbd0
+
+Combine multiple devices::
+
+  nsh> getevent -m /dev/mouse0 -t /dev/input0 -k /dev/kbd0
+
+Show help::
+
+  nsh> getevent -h
+
+Press ``Ctrl+C`` to stop monitoring.
+
+How It Works
+============
+
+When started without arguments, ``getevent`` scans ``/dev`` for character
+devices matching known input device name patterns (``mouse*``, ``input*``,
+``kbd*``). Each detected device is opened in non-blocking mode.
+
+The main event loop uses ``poll()`` with a 500 ms timeout to wait for data on
+all open file descriptors. When an event is available, the corresponding read
+callback decodes and prints the event structure via ``syslog``.
+
+``SIGINT`` (``Ctrl+C``) is handled to allow graceful shutdown with proper
+resource cleanup.
+
+Example Output
+==============
+
+Mouse event::
+
+  [getevent]: mouse event: /dev/mouse0
+  [getevent]:    buttons : 01
+  [getevent]:          x : 120
+  [getevent]:          y : 340
+
+Touch event::
+
+  [getevent]: touch event: /dev/input0
+  [getevent]:    npoints : 1
+  [getevent]: Point      : 0
+  [getevent]:      flags : 03
+  [getevent]:          x : 200
+  [getevent]:          y : 450
+  [getevent]:  timestamp : 123456789
+
+Keyboard event::
+
+  [getevent]: keyboard event: /dev/kbd0
+  [getevent]:          type : 1
+  [getevent]:          code : 28

Documentation/applications/graphics/input/index.rst

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+=============
+Input Support
+=============
+
+.. toctree::
+   :maxdepth: 1
+   :titlesonly:
+   :caption: Contents
+
+   getevent