feat: node-to-node MJPEG streaming CLIs and shared V4L2 format header

Add stream_send_cli (V4L2 capture → TCP → VIDEO_FRAME) and
stream_recv_cli (TCP → threaded frame slot → GLFW display) to
exercise end-to-end streaming between two nodes on the same machine
or across the network.

Add include/stream_stats.h (header-only rolling-window fps/Mbps tracker)
and include/v4l2_fmt.h (header-only V4L2 format enumeration shared between
v4l2_view_cli and stream_send_cli). Refactor v4l2_view_cli to use the
shared header.

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

planning.md

@@ -82,6 +82,8 @@ Each module gets a corresponding CLI driver that exercises its API and serves as
 | `test_image_cli` | `test_image` | Generate test patterns, write PPM for visual inspection |
 | `xorg_cli` | `xorg` | Display test pattern in viewer window; exercises scale/anchor modes and text overlays |
 | `v4l2_view_cli` | V4L2 + `xorg` | Live camera viewer — auto-selects highest-FPS format, FPS/format overlay; bypasses node system |
+| `stream_send_cli` | V4L2 + `transport` + `protocol` | Capture MJPEG from V4L2, connect to receiver, send VIDEO_FRAME messages; prints fps/Mbps stats |
+| `stream_recv_cli` | `transport` + `protocol` + `xorg` | Listen for incoming VIDEO_FRAME stream, display in viewer; fps/Mbps overlay; threaded transport→GL handoff |
 
 ### Web UI (`dev/web/`)