Add dev/web to plan; expand dev tools section and directory structure

- dev/web/ is the browser-side equivalent of dev/cli/ — a Node.js dev UI
  that speaks the binary protocol and exposes V4L2/topology inspection
- Explicitly noted as blocked on transport+protocol being finalised
- Distinguished from the future production dashboard
- Directory structure updated to show serial/transport/protocol modules

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

planning.md

@@ -17,10 +17,15 @@ video-setup/
       common/        - shared definitions (error types, base types)
       media_ctrl/    - Linux Media Controller API (topology, pad formats, links)
       v4l2_ctrl/     - V4L2 camera controls (enumerate, get, set)
+      serial/        - little-endian binary serialization primitives
+      transport/     - framed TCP stream, single-write send
+      protocol/      - typed write_*/read_* message functions
     node/            - video node entry point and top-level integration (later)
   include/           - public headers
   dev/
     cli/             - exploratory CLI drivers, one per module
+    web/             - development web UI (Node.js/Express); browser-side equivalent
+                       of the CLI tools; depends on protocol being finalised
     experiments/     - freeform experiments
   tests/             - automated tests (later)
   Makefile
@@ -51,9 +56,11 @@ Modules are listed in intended build order. Each depends only on modules above i
 
 ---
 
-## Dev CLI Drivers
+## Dev Tools
 
-Each module gets a corresponding CLI driver in `dev/cli/` that exercises its API and serves as both an integration check and a useful development tool.
+### CLI (`dev/cli/`)
+
+Each module gets a corresponding CLI driver that exercises its API and serves as both an integration check and a useful development tool.
 
 | Driver | Exercises | Notes |
 |---|---|---|
@@ -61,6 +68,14 @@ Each module gets a corresponding CLI driver in `dev/cli/` that exercises its API
 | `v4l2_ctrl_cli` | `v4l2_ctrl` | List controls, get/set values — lightweight `v4l2-ctl` equivalent |
 | `transport_cli` | `transport` | Send/receive framed messages, inspect headers |
 
+### Web UI (`dev/web/`)
+
+A Node.js/Express development web UI — the browser-side equivalent of the CLI tools. Connects to a running video node as a binary protocol peer and exposes its capabilities through a browser interface: V4L2 control inspection and adjustment, media topology view, stream state.
+
+**Prerequisite**: the `transport` and `protocol` modules must be finalised before `dev/web/` can be implemented — the web UI depends on a stable wire format and a `protocol.mjs` that mirrors the C protocol module.
+
+This is a development aid, not the production dashboard. The production dashboard (full stream configuration UI) is a later, separate project.
+
 ---
 
 ## Future: Protocol Preprocessor