docs: restructure documentation into MkDocs Material site

docs/reference/api/tracks.md

@@ -0,0 +1,14 @@
+# Tracks API
+
+Auto-generated reference for the track model: [`Tracks`][unshackle.core.tracks.Tracks],
+[`Track`][unshackle.core.tracks.Track], and the media-specific subclasses. See
+[Service Architecture](../../dev/service-architecture.md) for how these fit together.
+
+::: unshackle.core.tracks
+    options:
+      show_root_heading: false
+      show_source: false
+      members_order: source
+      heading_level: 2
+      filters:
+        - "!^_"