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).
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