tools/demo-video: regenerate the README demo from an MCP session with the app

An I-beam cantilever from the corpus is opened, hex meshed, defined, solved and shown with von
Mises contours and a swinging deformed shape, every step an MCP tool call bridged to the
desktop app and every picture the MCP screenshot of the window; ffmpeg encodes the MP4 and GIF.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

tools/demo-video/README.md

@@ -0,0 +1,36 @@
+# Demo video
+
+`make.py` regenerates the README's demo, `docs/media/ibeam-analysis.mp4` and
+`docs/media/ibeam-analysis.gif`: an agent analyses an I-beam cantilever over MCP while the
+desktop app shows each step.
+
+```sh
+python3 tools/demo-video/make.py                  # build, run, encode into docs/media
+python3 tools/demo-video/make.py --no-build       # with the release binaries already built
+python3 tools/demo-video/make.py --frames /tmp/f  # also keep the captured pictures
+```
+
+Needs Python 3 (standard library only), a display for the app window (the pictures are drawn
+offscreen, so a locked screen is fine) and `ffmpeg` with libx264 on the `PATH` (or `FFMPEG`).
+It honours `CARGO_TARGET_DIR`.
+
+What it does:
+
+1. Builds `modelcraft`, `modelcraft-cli` and the testkit's `corpus` tool (release).
+2. Writes the corpus I-beam (`tests/corpus/i-beam`) as a `.solidcraft` design to a temporary
+   folder with `corpus --part i-beam --design`.
+3. Starts the app with `--control PORT` and `modelcraft-cli mcp --connect 127.0.0.1:PORT`, and
+   speaks MCP (JSON-RPC over stdio) to it. Every step is an MCP tool call: `open` the design,
+   `mesh` (`hex_sweep`, 4 mm), `batch` (steel, a solid section, the root clamp, a kinematic
+   coupling of the free end to a reference point loaded with 1000 N), `check_model`, `solve`
+   (`static`), and `show_results` for the von Mises contours and the deformed shape, its `scale`
+   stepped from 1 to 150 and back. Every picture is the MCP `screenshot` tool with
+   `source: window` (the whole window drawn offscreen, `ui.capture`), turned to the `iso` or
+   `right` view by its `view` argument.
+4. Encodes the pictures at 10 frames per second, each held for its stage, into the MP4 (H.264,
+   1280 px) and the GIF (960 px, its own palette), and prints the tip deflection and the peak
+   von Mises stress.
+
+The theme is the app's default (dark). Beam theory for the same beam gives a tip deflection of
+0.143 mm in bending plus about 0.034 mm in shear (0.177 mm) and a root bending stress of 45 MPa;
+the clamped root adds a local peak above that.