feat(app,player): page fade, Ctrl+S screenshots

- a page fades in over 140 ms when the page changes, rather than cutting
- Ctrl+S in the player saves the frame, without subtitles, to
  Pictures/proton-stream as "Title  S01E04  12-34.png"

crates/pstr-app/Cargo.toml

@@ -29,6 +29,7 @@ sha2.workspace = true
 parking_lot.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+directories.workspace = true
 souvlaki.workspace = true
 
 [target.'cfg(target_os = "linux")'.dependencies]