docs: write CLI docs for all 12 previously undocumented tools

Add docs/cli/ entries for:
  transport_cli, discovery_cli, config_cli, protocol_cli, query_cli,
  test_image_cli, xorg_cli, v4l2_view_cli, stream_send_cli,
  stream_recv_cli, reconciler_cli, controller_cli

Each doc covers: description, build instructions, full usage with all
options and defaults, example output, and a relationship note pointing
to related tools. controller_cli includes the display control IDs table
and notes its temporary status.

README.md: convert all CLI tool entries to links.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/cli/xorg_cli.md

@@ -0,0 +1,73 @@
+# xorg_cli
+
+A development tool for testing the xorg viewer sink. Opens an X11 window using GLFW/OpenGL, renders a test pattern at the chosen scale and anchor, and displays a text overlay showing the current date. The window stays open until the user presses Q, Escape, or closes it.
+
+---
+
+## Build
+
+From the repository root:
+
+```sh
+make cli
+```
+
+The binary is placed in `build/cli/`.
+
+Requires the GLFW, OpenGL, and libjpeg-turbo libraries. If compiled without `HAVE_GLFW`, the binary will print an error and exit.
+
+---
+
+## Usage
+
+```sh
+./xorg_cli [--pattern bars|ramp|grid]
+           [--width N] [--height N]
+           [--format yuv420|bgra]
+           [--scale stretch|fit|fill|1:1]
+           [--anchor center|topleft]
+           [--x N] [--y N]
+```
+
+| Option | Default | Description |
+|---|---|---|
+| `--pattern` | `bars` | Test pattern to render |
+| `--width N` | `1280` | Window width in pixels |
+| `--height N` | `720` | Window height in pixels |
+| `--format` | `yuv420` | Frame pixel format |
+| `--scale` | `stretch` | How the frame fills the window |
+| `--anchor` | `center` | Frame alignment within the window |
+| `--x N` | `0` | Window X position on screen |
+| `--y N` | `0` | Window Y position on screen |
+
+### Scale modes
+
+| Mode | Description |
+|---|---|
+| `stretch` | Fill the window, ignoring aspect ratio |
+| `fit` | Largest rect that fits, preserving aspect ratio (black bars) |
+| `fill` | Smallest rect that covers, preserving aspect ratio (crops edges) |
+| `1:1` | Native pixel size, no scaling |
+
+### Anchor modes
+
+Anchor applies when the frame does not fill the window (fit, fill, 1:1 modes):
+
+| Mode | Description |
+|---|---|
+| `center` | Centre the frame in the window |
+| `topleft` | Align frame to the top-left corner |
+
+### Example
+
+```sh
+./xorg_cli --pattern grid --scale fit --anchor center --width 1920 --height 1080
+```
+
+---
+
+## Relationship to the Video Routing System
+
+`xorg_cli` exercises the `xorg` module used by the video node for its display sink role. The same viewer, scale/anchor logic, and text overlay system are used by `stream_recv_cli` and the node's `START_DISPLAY` command.
+
+See also: [`v4l2_view_cli.md`](v4l2_view_cli.md) for live camera feed display; [`stream_recv_cli.md`](stream_recv_cli.md) for network stream display.