docs: the umbrella-index edit belongs on scadaproj's main, and must be pushed

The cross-repo propagation rule said WHAT to update but not WHERE. scadaproj is
a separate repo with its own checkout, so committing there inherits whatever
branch it happens to be on — usually an unrelated feature branch, sometimes one
with no upstream — and the index then disagrees with reality for as long as that
branch stays unmerged.

Observed 2026-07-27: the Sql poll driver's index entry had sat unpushed on
feat/overview-dashboard since 2026-07-24 despite this rule, and the Mqtt driver's
entry was about to join it. Both recovered by cherry-picking onto main.

Records the explicit procedure and says to cherry-pick stranded index commits
rather than merge the branch they are stuck on. The canonical statement now also
lives in scadaproj's own CLAUDE.md (main @ 75f267c).

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

CLAUDE.md

@@ -55,6 +55,28 @@ about OtOpcUa changes here — remote/push status, the driver set, the Galaxy da
 shared-lib consumption, or per-project commands — update the **OtOpcUa entry in
 `../scadaproj/CLAUDE.md`** in the same change so the index never drifts from this repo.
 
+**The index edit belongs on `scadaproj`'s `main`, and must be pushed.** `scadaproj` is a
+separate repo with its own checkout, so committing there inherits whatever branch it
+happens to be on — which is usually *not* `main` and is often an unrelated feature branch
+with no upstream. That silently drifts the index for as long as that branch stays
+unmerged, which is the exact failure the rule above exists to prevent. Do this explicitly:
+
+```bash
+cd ~/Desktop/scadaproj
+git rev-parse --abbrev-ref HEAD            # note it, to restore afterwards
+git stash list                             # never commit onto a dirty unrelated branch
+git checkout main && git pull
+#   …edit the OtOpcUa entry in CLAUDE.md…
+git commit -am "docs(index): <what changed about OtOpcUa>"
+git push origin main
+git checkout -                             # restore the original branch
+```
+
+Observed 2026-07-27: the `Sql` poll driver's index entry had sat unpushed on an unrelated
+feature branch since 2026-07-24 because it was committed onto the current checkout, so the
+index disagreed with reality for three days despite this rule. If you find index commits
+stranded on a feature branch, cherry-pick them onto `main` rather than merging that branch.
+
 ## Architecture Overview
 
 ### Data Flow