Fit the page on startup, name the bundle, show the selection

Three things a first session trips over.

The editor opened at an arbitrary zoom. show_page does fit the page, but
it runs before the window has been laid out, when the viewport is still
its default size; redo it once when the real size arrives.

The bundle was named after the PDF, which is whatever the download was
called. Take the song's title instead — unsafe characters dropped, then
whitespace collapsed to dashes. Accented letters stay, since ä and ö are
not a filesystem's problem, but a leading dot would hide the file.

And the selected slice was drawn as an outline whose top and bottom edges
run under the cut lines painted over them, leaving two thin verticals in
the margins and no way to tell what was selected. Wash the slice, as the
discard and engraved states already do, and keep the outline for the trim
anomalies it exists to show.

tests/test_editor.py

@@ -19,6 +19,7 @@ sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
 
 from PySide6.QtWidgets import QApplication  # noqa: E402
 
+from noteman_slicer import bundle  # noqa: E402
 from noteman_slicer.detect import detect_page  # noqa: E402
 from noteman_slicer.editor import Editor  # noqa: E402
 from noteman_slicer.pdf import open_source, page_raster  # noqa: E402
@@ -105,6 +106,28 @@ def main() -> int:
     assert reloaded.pages[0].levels == (40, 210)
     assert [c.points for c in reloaded.pages[0].cuts] == [c.points for c in page.cuts]
 
+    # The page fits the viewport once the window has a real size. show_page's
+    # own fit runs before layout, when the viewport is still its default.
+    editor.resize(900, 700)
+    editor.show()
+    app.processEvents()
+    scene = editor.view.sceneRect()
+    scale = editor.view.transform().m11()
+    viewport = editor.view.viewport()
+    fill = max(
+        scale * scene.width() / viewport.width(),
+        scale * scene.height() / viewport.height(),
+    )
+    # Fit means nearly touching one edge — Qt leaves a small margin of its own.
+    # A "≤ 1" check alone would pass a page zoomed down to a dot.
+    assert 0.9 <= fill <= 1.02, f"page is not fitted to the window: {fill:.3f}"
+
+    # The bundle is named after the song, not the PDF.
+    assert bundle.filename(project) == "Ketun-joululaulu.zip"
+    project.metadata["title"] = "AC/DC: T.N.T. (live)"
+    assert bundle.filename(project) == "ACDC-T.N.T.-live.zip"
+    project.metadata["title"] = "Ketun joululaulu"
+
     editor.close()
     source.close()
     for f in (pdf, saved):