#18 — Image compression benchmark

[hajk1]

Script scripts/benchmark_compression.py comparing JPEG (q50/75/95), WebP, and PNG on a set of synthetic greenhouse images. Informs the recommended format for spider SD card storage.

Acceptance criteria:

• Reports: format, quality, compressed size, ratio vs raw, encode ms, decode ms
• ≥10 sample images (can be synthetically generated with numpy)
• Recommended format committed to docs/compression_benchmark.md with rationale
• Script runs on RPi3B+ without extra dependencies