SEC-2: write down the release path, now that master refuses a direct push

master is the default branch, which is what the Home Assistant Supervisor
clones - so whatever sits on it runs on a real 5 kW inverter. Until today it
had no branch protection at all, while every gate this repo built sat on
release/1.0, the branch that does not ship. 0.10.1 went straight onto master
on 2026-09-22 with no PR, no CI and no reviewer, and it succeeded.

master now carries the same rule as release/1.0 - enable_push false,
required context `checks / unit (pull_request)`, block_admin_merge_override,
required_approvals 0. That is a forge setting and cannot live in a commit, so
the part that can is this: the procedure it implies. Without it the next
release is attempted the old way and fails confusingly at the push.

docs/RELEASE.md records the path (merge to release/1.0, bump version, PR
release/1.0 -> master, wait for green, merge, then `ha store reload` before
the Supervisor offers anything), the before/after protection state of both
branches, and how the gate was proven to bite rather than merely badge green.

Documentation only - no code, no workflow change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

README.md

@@ -33,6 +33,8 @@ estop/rs485_log.py           optional RS485 e-stop / bus witness
 docs/GoodWe-RS485-Field-Guide.pdf  the guide techs carry (10pp, A4)
 docs/build_guide.py          its single source - rebuilds the HTML and PDF
 FIELD-GUIDE.md             how to edit and rebuild the guide
+docs/RELEASE.md            how a change reaches the battery - `master` is
+                           protected, releases go via PR from `release/1.0`
 ```
 
 **Picking this up after a break? Read `HANDOVER.md` first** — current state,