feat: persist note list sort preference in type file frontmatter

Sort preferences for each type's note list are now stored in the type
file's frontmatter (e.g. `sort: modified:desc` in `type/person.md`)
instead of localStorage. This makes preferences portable with the vault
and versionable in git.

- Add `sort` field to Rust Frontmatter/VaultEntry and TS VaultEntry
- NoteList reads sort from type entry's frontmatter when viewing a type
- Sort changes write to type file via update_frontmatter
- Silent migration from localStorage on first access per type
- Relationship group sorts still use localStorage (no type file)
- Fallback to `modified:desc` when no sort preference exists

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useNoteListKeyboard.test.ts

@@ -22,7 +22,7 @@ function makeEntry(path: string, title: string): VaultEntry {
     fileSize: 100,
     color: null,
     icon: null,
-    template: null,
+    template: null, sort: null,
     outgoingLinks: [],
     relationships: {},
   }