ESFEX v0.1.9

Patch release fixing four issues found in v0.1.8.

Fixes

• In-app documentation now renders. The docs are bundled into the
  package at build time, so the Studio documentation viewer works in
  pip-installed environments (it previously came up empty).
• Toolbar icon upscaling is capped so the responsive toolbar grows
  to fill wide windows without ever becoming oversized.
• Windows installer is built on the release: published event (the
  same trigger as the PyPI publish), so publishing a release always
  builds and attaches the installer — no missed or duplicated builds.
• Dropped the unused pypowsybl dependency. The PowSyBl-based SLD
  engine was reverted in favour of the custom engine; its heavy
  dependency and dead code are removed, so the package no longer pulls
  in pypowsybl.

The Windows installer (ESFEX-0.1.9-Windows-x86_64.exe) is attached once
the build finishes. `pip install -U esfex` for the Python package.