Add GitHub Actions CI + Windows notes on the developer docs

GitHub had no CI, so naming/tests/build were unenforced on the public
mirror. Add .github/workflows/ci.yml mirroring the internal pipeline:
backend pytest, the naming gate, frontend vitest+build, and the
migrations-mysql job that proves a fresh flask db upgrade + every
plugin chain on utf8mb4 MySQL 8 is idempotent. Flip the dev-setup CI
note to reflect it. Add an identical Windows/VS Code convention note to
the four developer docs (venv\Scripts vs venv/bin, $env: vs export,
pointer to DEVELOPMENT-SETUP).

docs/PLUGIN-LAB-PRINTEDPARTS.md

@@ -14,6 +14,12 @@ badge-scanned employee, a touch kiosk (scan bin barcode, scan badge, keypad
 quantity), 1x0.5in bin labels, low-stock email alerts, and reports. Spec with
 decision records: `docs/proposals/printedparts-plugin.md`.
 
+> **Windows / VS Code:** command examples below use the Linux venv path
+> `venv/bin/python`; on Windows use `venv\Scripts\python` and
+> `$env:FLASK_APP="shopdb"` (not `export`). Full Windows onboarding:
+> [DEVELOPMENT-SETUP](DEVELOPMENT-SETUP).
+
+
 Know before you start
 - BUNDLED plugin: frontend files live in core `frontend/src/`, and three core
   files get small edits (api client, sidebar icon map, PLUGIN_TABLE_OWNERS).