docs: branch model documents one branch per instance

CONTRIBUTING.md still said "main is the product every site runs and the
publication mirror exports" and framed wj/wilm as site branches feeding it.
That was true when main was the only thing anyone deployed. It is not now:
WJ production runs wj, the /ops instance runs dev, and main deploys nowhere.
Nothing in the repository mentioned dev at all, so the branch a deploy script
refuses to run without was undocumented.

Replaces that section with the branch/instance table and the dev -> wj -> main
promotion order, and says why promoting before validating is the wrong way
round. Keeps the wilm note but moves it up with the reason it cannot be
merged locally: it sits on the publication lineage and shares no ancestor.

CLAUDE.md gains the branch-to-server pointer and records that
export-github.sh now builds a dist only for wj and dev.

docs/DEPLOY.md is deliberately left alone: `git pull origin main` is correct
there. That document is the generic connected-Docker deploy another site
follows, and main is exactly what another site adopts.

Scope: product

CLAUDE.md

@@ -36,6 +36,7 @@ should be typed here again.
 | what the collector sends | `docs/COLLECTOR-INTEGRATION.md`, ADR-006 |
 | how a site is deployed | `docs/INSTALL-WINDOWS.md`, `docs/OPERATE-WINDOWS.md` |
 | how code reaches GitHub | `tools/export-github.sh` |
+| which branch reaches which server | `devnotes/deploy-and-branch-model.html` |
 
 ## Standards are gates, not prose
 
@@ -102,7 +103,9 @@ surface and always ships.
 - `shopdb/plugins/loader.py` - discovery and dependency-aware loading
 - `shopdb/plugins/alembic_template.py` - the env every plugin chain runs through
 - `frontend/src/router/index.js`, `frontend/src/components/AppSidebar.vue`
-- `tools/export-github.sh` - scrub and publication gate
+- `tools/export-github.sh` - scrub and publication gate; builds the dist for
+  the branch it is on (`wj` -> /shopdb, `dev` -> /ops) and refuses on any other
+- `tools/mirror-wilm.sh` - push a carried wilm bundle to gitea
 
 ## State