feat: recommend server-generated mixes from Musify and YouTube Music

Mixes are their own concept, not playlists: they live in their own
Mixes/MixItems tables, cannot be edited and never show up among the
user's playlists. Each item is either a Musify track or a YouTube Music
reference, so YouTube songs stream directly instead of being downloaded.

A daily Hangfire job seeds the mixes from the listening history: one
discovery mix, one daily mix and one per top artist.

The per-user YouTube filler query was already in the working tree and
rides along here because it shares files with this change.

web-player/src/lib/api/schema.d.ts

@@ -126,6 +126,40 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/mixes": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /** Get The Server-Generated Mixes Of The Current User. */
+        get: operations["GetMixes"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+    "/mixes/{id}": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /** Get A Mix With All Of Its Songs. */
+        get: operations["GetMixById"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/playlists": {
         parameters: {
             query?: never;
@@ -585,6 +619,31 @@ export interface components {
                 [key: string]: string[];
             };
         };
+        MixApplicationResponse: {
+            /** Format: uuid */
+            id: string;
+            title: string;
+            subtitle: null | string;
+            /** Format: date */
+            generatedOn: string;
+            /** Format: int32 */
+            itemCount: number | string;
+            items: components["schemas"]["MixItemApplicationResponse"][];
+        };
+        MixItemApplicationResponse: {
+            source: components["schemas"]["MixItemSource"];
+            /** Format: uuid */
+            trackId: null | string;
+            videoId: null | string;
+            title: string;
+            artist: null | string;
+            thumbnailUrl: null | string;
+            /** Format: int32 */
+            durationSeconds: number | string;
+            isExplicit: boolean;
+        };
+        /** @enum {unknown} */
+        MixItemSource: "Musify" | "YouTube";
         PaginatedResponseOfAlbumApplicationResponse: {
             items: components["schemas"]["AlbumApplicationResponse"][];
             /** Format: int32 */
@@ -1184,6 +1243,69 @@ export interface operations {
             };
         };
     };
+    GetMixes: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["MixApplicationResponse"][];
+                };
+            };
+            /** @description Unauthorized */
+            401: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+        };
+    };
+    GetMixById: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                id: string;
+            };
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["MixApplicationResponse"];
+                };
+            };
+            /** @description Unauthorized */
+            401: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+            /** @description Not Found */
+            404: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+        };
+    };
     GetPlayLists: {
         parameters: {
             query?: {