Add AGENTS.md for Cursor Cloud dev environment setup

[endolith]

Summary

Adds AGENTS.md with Cursor Cloud specific development environment instructions, including:

• Conda environment setup details (PDAL requires native C++ libraries via conda-forge)
• Server startup instructions (SSL cert generation + Flask HTTPS server)
• Manual testing guidance (curl commands for requesting tiles)
• Key gotchas (cert regeneration, AWS fetch latency, zoom-level restrictions)

Environment Setup Verified

The full development environment was set up and verified end-to-end:

1. Miniforge/conda installed with lidar environment containing all dependencies (PDAL, Flask, geopandas, rioxarray, etc.)
2. SSL certificates generated via generate_cert.py
3. Flask HTTPS tile server started successfully on port 5000
4. LiDAR tile request completed successfully -- fetched point cloud data from AWS S3 for the Washington DC area, processed it into a DSM, and returned a 510x512 PNG tile

Demo tile (DC area, zoom 18)

LiDAR DSM tile of Washington DC area

Server logs showing successful pipeline execution

Server log output

_{To show artifacts inline, enable in settings.}