Release 0.8.1

The installer on the share was stamped 0.8.0 and contained sixteen commits that
were not in the v0.8.0 tag. A build that misreports its own version is exactly
what the version check in docs/RELEASING-WINDOWS.md exists to prevent, and it
would have left two sites unable to say what they were running.

Everything in 0.8.1 landed after v0.8.0 was tagged this morning, driven by two
sites entering real data for the first time: the blank-code 500, the two-slide
display that never rotated, modals discarding a part-filled form, filters
returning an empty page, model photos that could not be saved, and the shared
equipment catalog that lets a new site start with vendors, models and printer
supply part numbers already present.

CHANGELOG gains a 0.8.1 section, and the OpenAPI document follows __version__
rather than being restated.

docs/openapi.json

@@ -2,7 +2,7 @@
  "openapi": "3.1.0",
  "info": {
   "title": "ShopDB Flask API",
-  "version": "0.8.0",
+  "version": "0.8.1",
   "description": "Asset-management API (core + plugins). Responses use a `success_response` envelope: `{status, data, meta}`. Auth: Bearer JWT (login or a managed PAT) for `jwt`/`admin`/`permission:*`; `X-API-Key` for collector/managed-token endpoints; public endpoints need neither."
  },
  "servers": [