Step 5 of the gui/app.py + gui/preview.py structural refactor. Moves
the click-to-seek QSlider variant and the mpv-backed transport-control
widget into their own module under media/. The new module imports
_MpvGLWidget from .mpv_gl (sibling) instead of relying on the bare
name in the old preview.py namespace.
Address-only adjustment: the lazy `from ..core.cache import _referer_for`
inside `play_file` becomes `from ...core.cache import _referer_for`
because the new module sits one package level deeper. Same target
module, different relative-import depth — no behavior change.
preview.py grows another re-export shim line so ImagePreview (still
in preview.py) and FullscreenPreview can keep constructing
VideoPlayer unchanged. Shim removed in commit 14.
Step 4 of the gui/app.py + gui/preview.py structural refactor. Pure
move: the OpenGL render-context host and its concrete QOpenGLWidget
companion are now in their own module under media/. The mid-file
`from PySide6.QtOpenGLWidgets import QOpenGLWidget as _QOpenGLWidget`
import that used to sit between the two classes moves with them to
the new module's import header. preview.py grows another re-export
shim line so VideoPlayer (still in preview.py) can keep constructing
_MpvGLWidget unchanged. Shim removed in commit 14.
Step 3 of the gui/app.py + gui/preview.py structural refactor. Pure
move: the zoom/pan image viewer class is now in its own module under
media/. preview.py grows another re-export shim line so ImagePreview
and FullscreenPreview (both still in preview.py) can keep constructing
ImageViewer instances unchanged. Shim removed in commit 14.
Step 1 of the gui/app.py + gui/preview.py structural refactor. Pure
move: the constant and predicate are now in their own module, and
preview.py grows a re-export shim at the bottom so existing imports
(app.py:1351 and the in-file class methods) keep working unchanged.
Shim is removed in commit 14 once importers update to the canonical
path. See docs/REFACTOR_PLAN.md for the full migration order.
