Handover doc: state, known breakage, and what to do next

Written for a cold start. Covers what is actually running (0.2.0, on a real
battery), how to deploy without falling into the version-bump trap, the four
things that are known broken, and the ranked next steps.

Leads with the two facts most likely to cause harm if missed: never run the
add-on and the old YAML packages together, and a "-20"/G2 inverter cannot be
driven by this at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016NckgXecasQb2eSsPYNSW6

README.md

@@ -26,6 +26,9 @@ docs/build_guide.py          its single source - rebuilds the HTML and PDF
 FIELD-GUIDE.md             how to edit and rebuild the guide
 ```
 
+**Picking this up after a break? Read `HANDOVER.md` first** — current state,
+what is known broken, and what to do next.
+
 ## Install
 
 Settings → Add-ons → Add-on store → ⋮ → **Repositories** → add