Add Cursor Cloud dev environment setup notes (AGENTS.md)

[grebmeg]

Summary

Sets up and documents the development environment for this Vello Cargo workspace so Cursor Cloud agents can build, lint, test, and run the renderers. No application code is modified — this PR only adds AGENTS.md.

Environment provisioning done in the VM (captured in the snapshot; not application changes):

• Installed Rust stable 1.96 toolchain (repo needs edition 2024 / MSRV 1.88; Ubuntu default rustc 1.83 is too old) + wasm32-unknown-unknown target, clippy, rustfmt.
• Installed native deps: libfontconfig-dev, libasound2-dev, libudev-dev, g++, plus mesa-vulkan-drivers (lavapipe software Vulkan), vulkan-tools, xvfb.
• Installed cargo-nextest.
• Pointed cc/c++ alternatives to gcc/g++ so nv-flip-sys (used by vello_tests) links against libstdc++.

Update script (dependency refresh on startup): cargo fetch --locked.

What was verified

Check	Command	Result
Build	cargo build --workspace	pass
Format	cargo fmt --all --check	pass
Lint	cargo clippy --workspace	pass
CPU tests	cargo nextest run -p vello_cpu -p vello_common -p glifo --release	256 passed
GPU snapshot tests	cargo nextest run -p vello_tests --release (lavapipe)	64 passed
CPU render	cargo run -p vello_cpu --example basic	wrote PNGs
GPU render	cargo run -p headless -- --test-scenes -s 0 (lavapipe)	rendered GhostScript Tiger

Hello-world artifacts

GPU renderer (software Vulkan / lavapipe) rendering the flagship GhostScript Tiger test scene:

GPU headless tiger render

CPU renderer (vello_cpu) basic shapes example:

CPU basic shapes render

  

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
_{Learn more about Cursor Agents}