Make HAGR the gateway to maintained grow-room projects

[JakeTheRabbit]

Strategy

Keep HAGR as the established ecosystem landing page and implementation archive. Preserve every inbound URL, but route readers to the maintained specialist repo for new work. GitHub Markdown files cannot issue HTTP redirects, while replacing or renaming the repository would risk HAGR's existing search and backlink value.

What changed

• turns PARTS_LIST.md into a permanent signpost to Awesome Grow Room Parts
• adds a current-project map at the top of the high-traffic root README
• routes crop steering, Athena calculations, substrate sensing, Thermal2 firmware, cultivation guides, dashboards, and grow records to their maintained repos
• marks legacy package and firmware paths without deleting them
• removes dead, private, or unrelated repos from the public related-project table
• corrects three stale local links
• corrects the M5Stack Atom PWM description and link so it is not presented as an isolated 0-10 V interface

Merge order

Merge JakeTheRabbit/awesome-grow-room-parts#1 first. It fills the three gaps found when comparing the old HAGR parts list with the new catalogue.

Verification

• all local links in the seven changed Markdown files resolve
• all 12 promoted successor repositories are public
• the Awesome Grow Room Parts, Athena calculator, and Cannabis White Papers Pages sites return HTTP 200
• git diff --check passes