docs(ci): add AGENTS.md with Cursor Cloud setup notes

[incrementaliser]

Summary

Sets up the Cursor Cloud development environment for dynamicsyntax (DyLan) and documents durable, non-obvious run/test caveats for future agents.

• Adds AGENTS.md with a ## Cursor Cloud specific instructions section covering the product surfaces (library, induction CLI, Flet GUI, Pyodide web shell) and gotchas.
• Environment uses uv; the startup update script is uv sync --group dev --python 3.11.

Verified in this environment

• uv run ruff check tests — lint passes.
• uv run pytest -q — 243 passed, 4 skipped.
• uv build — builds wheel + sdist.
• Library parse (ds.parse("a man knows you", "ttr")) — produces TTR semantics + parse tree.
• uv run dsttr-induction --config configs/induction/holdout.yaml — trains + evaluates (100% F1 on BabyDS class1).
• Flet GUI (DYLAN_FLET_WEB=1 uv run dylan-gui) — renders and is interactive in the browser.

Known limitations (pre-existing, not environment/setup issues)

• Pyodide web shell: bundled micropip rejects the wheel served as package.whl (InvalidWheelFilename), so Python fails to boot in the browser — a code-level issue in web/app.js / scripts/sync_web_wheel.py.
• Flet GUI in web mode: the "Load grammar" button uses a native directory picker that doesn't work in a browser, so grammar loading can't complete via the web GUI; use the library/CLI (or native desktop mode) for end-to-end parsing.

Demo

Hello-world parse of "a man knows you" producing TTR semantics + parse tree:

dylan_parse_hello_world_demo.mp4

Flet GUI running in the browser:

Flet GUI running

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