behavior change: stop() now calls _gl_widget.release_render_context()
after dropping hwdec, which frees the MpvRenderContext's internal
textures and FBOs. Previously the render context stayed alive for the
widget lifetime — its GPU allocations accumulated across video-to-image
switches in the stacked widget even though no video was playing.
The context is recreated lazily on the next play_file() via the
existing ensure_gl_init() path (~5ms, invisible behind network fetch).
After release, paintGL is a no-op (_ctx is None guard) and mpv won't
fire frame-ready callbacks, so the hidden QOpenGLWidget is inert.
cleanup() now delegates to release_render_context() + terminate()
instead of duplicating the ctx.free() logic.
pax
eab805e705