v2.19.0

FireFlow 2.19.0 — the project is renamed, and the slug breaks with it

spotymod is now FireFlow. This release is the rename: the plugin slug, the
module slug, the faceplate wordmark, the repository and the release assets all
change together.

BREAKING — existing patches lose the module. The plugin and module slug go
Spotymod -> Fireflow, and VCV identifies saved modules by slug. A patch built
with spotymod will open with the module missing unless the old spotymod plugin
folder stays installed alongside this one; kept side by side, both load and old
patches keep working.

Assets are now Fireflow-2.19.0-<platform>.vcvplugin. Releases up to 2.18.x keep
the Spotymod name and are unaffected.

No engine change. The DSP, the panel layout and every control are identical to
2.18.3 — only names moved.