docs: add AGENTS.md with Cursor Cloud dev environment setup

[Web3Capital]

Summary

Sets up and verifies the Cloud Agent development environment for this repository, and documents it for future agents.

This project is a zero-dependency, zero-build static website — an interactive linear-algebra teaching site written in plain HTML / CSS / vanilla JavaScript (ES Modules). There is no package manager, lockfile, bundler, lint, or automated test suite.

What was done

• Verified the runtime: python3 3.12.3 is preinstalled; nothing needs installing.
• Ran the dev server (python3 -m http.server 8000) and confirmed all assets serve with HTTP 200.
• Performed an end-to-end "hello world" interaction test in Chrome (see below).
• Added AGENTS.md with a ## Cursor Cloud specific instructions section capturing durable, non-obvious notes (must be served over HTTP because of ES Modules, no lint/test/build, the favicon 404 is harmless, GitHub Pages deploy is upload-only).
• Configured the VM update script to python3 --version (validation only — there are no dependencies to install).

How to run

python3 -m http.server 8000
# open http://localhost:8000/

Verification

The site loads (5-lesson sidebar + interactive canvas), lesson navigation works, the matrix-transform lesson animates the grid, and dragging a vector control point updates its magnitude/angle live. The only console message is a harmless favicon.ico 404.

linalg_site_hello_world_test.mp4

Initial vectors lesson
Matrix transform lesson
Dragging a vector control point

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