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/test_image_cli.md

@@ -0,0 +1,70 @@
+# test_image_cli
+
+A development tool for generating test images and writing them to PPM files. Used to verify the `test_image` module's pattern generators and pixel format output without needing a camera or display.
+
+---
+
+## Build
+
+From the repository root:
+
+```sh
+make cli
+```
+
+The binary is placed in `build/cli/`.
+
+---
+
+## Usage
+
+```sh
+./test_image_cli [--pattern bars|ramp|grid]
+                 [--width N] [--height N]
+                 [--format yuv420|yuv422|bgra]
+                 --out FILE.ppm
+```
+
+All options are optional except `--out`.
+
+| Option | Default | Description |
+|---|---|---|
+| `--pattern` | `bars` | Test pattern to generate |
+| `--width N` | `1280` | Image width in pixels |
+| `--height N` | `720` | Image height in pixels |
+| `--format` | `yuv420` | Internal pixel format before PPM conversion |
+| `--out FILE` | required | Output file path |
+
+### Patterns
+
+| Name | Description |
+|---|---|
+| `bars` | Colour bars (SMPTE-style) |
+| `ramp` | Luminance ramp from black to white |
+| `grid` | Crosshatch grid |
+
+### Formats
+
+| Name | Description |
+|---|---|
+| `yuv420` | Planar YUV 4:2:0 |
+| `yuv422` | Packed YUV 4:2:2 |
+| `bgra` | Packed BGRA 8-bit |
+
+The output is always written as a PPM (RGB) file regardless of format; the internal format affects how the pattern is generated and converted.
+
+### Example
+
+```sh
+./test_image_cli --pattern bars --width 1920 --height 1080 --format yuv420 --out bars.ppm
+```
+
+Open with any image viewer that supports PPM (e.g. `feh`, `eog`, GIMP).
+
+---
+
+## Relationship to the Video Routing System
+
+`test_image_cli` exercises the `test_image` module used by development tools to inject synthetic frames without a camera. The same module drives the xorg test pattern display in `xorg_cli`.
+
+See also: [`xorg_cli.md`](xorg_cli.md) for live window rendering.