feat(core,app): open the library the way it was last arranged

Filter, sort and franchise folding reset on every launch, so someone who
browses by Recently added chose it again each time. They are kept in the
desktop's own settings file, alongside the cache budget.

crates/pstr-core/src/browse.rs

@@ -11,7 +11,8 @@ use crate::library::{Library, Title, sort_name};
 use crate::metadata::{MetadataRecord, TitleNames};
 
 /// What order a grid is in.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "snake_case")]
 pub enum Sort {
     /// By the name shown, ignoring a leading article.
     #[default]