Release 0.12.0

Printers become a property of the bay, and the container stops throwing away the
site's own files every time it is updated.

Printer assignment is now end to end. The assignment belongs to the MACHINE and
reaches whichever PC controls it, so a reimaged or swapped bay comes back with
its printers and nothing had to be saved off the old box. One picker serves both
forms rather than two implementations of the same override. A relationship type
can declare itself singular, so setting a second default REPLACES the first
instead of silently losing to the older row. Alongside the assigned half there is
now an observed half: a bay reports what it actually has, kept strictly apart
from what it is told to have, because a drifted bay's own state becoming its
desired state would make every configuration error permanent. The client script
corrects a drifted queue in place rather than only installing a missing one, and
a driver rollout can be spread across waves so 300 bays do not pull 30 GB through
one five-minute window.

DOCKER SITES SHOULD READ THIS PARAGRAPH. The compose stack never persisted the
instance directory, so `docker compose build api && up -d api` - the update path
the docs themselves gave - discarded plugins.json and every upload with it. It is
a volume now, and DEPLOY.md carries the one-time rescue for a stack that predates
it. The image also could not be built at all: the frontend stage never copied the
plugin staging script its own prebuild hook runs, so every build since that
script landed failed. Air-gapped sites need a fresh offline bundle, because the
stack moves to MySQL 8.4 LTS and an existing tarball carries only the 8.0 image.

The Windows installer already bundled MySQL 8.4, so this closes a gap between the
two halves rather than moving anyone.

Adds a topology migration guide: IIS to Docker, Docker to a new host, and back.
The data moves cleanly; what costs time is that the server address is baked into
GE-Enforce manifests, the generated collector script, the printer client scripts
and printed QR codes.

1736 tests green. Contract stays at 0.20.0 - nothing under shopdb/api changed.

shopdb/__init__.py

@@ -63,7 +63,7 @@ __contract_version__ = '0.20.0'
 # plugin-contract version above are distinct series with independent
 # bump rules. Not part of the shopdb.api contract surface, so it is
 # not re-exported there.
-__version__ = '0.11.3'
+__version__ = '0.12.0'
 
 
 def create_app(config_name: str = None) -> Flask: