E frontend reconciliation (2/2): align consumers to generated bindings; svelte-check clean

Reconcile the ~50 frontend files that consumed the old hand-written types against
the stricter generated bindings (141 -> 0 svelte-check errors):

- Nullable strictness: null-coalesce/guard at consumer sites; widen shared helpers
  (CachedImage.tag, ticksToSeconds, formatDuration, getSessionIcon, session store
  send*/transferToRemote) to accept null.
- Field-name fixes exposed by codegen: userData.played -> isPlayed; remote
  NowPlayingItem uses album (not albumName); ArtistItem id/name.
- player.ts: normalize remote NowPlayingItem -> MediaItem in mergedMedia.
- ArtistItem now serializes camelCase (PascalCase alias retained for Jellyfin
  deserialize); update its serialize test.
- Update downloads.test.ts to the bundled { request } shape; complete the
  sessions.test.ts NowPlayingItem mock.

Frontend: svelte-check 0 errors, vitest 448 passing. Backend: 387 passing.

src/lib/stores/downloads.test.ts

@@ -80,14 +80,17 @@ describe("downloads store", () => {
       );
 
       expect(mockInvoke).toHaveBeenCalledWith("download_item", {
-        itemId: "item-1",
-        userId: "user-1",
-        filePath: "/path/to/file.mp3",
-        mimeType: "audio/mpeg",
-        priority: 10,
-        itemName: undefined,
-        artistName: undefined,
-        albumName: undefined,
+        request: {
+          itemId: "item-1",
+          userId: "user-1",
+          filePath: "/path/to/file.mp3",
+          mimeType: "audio/mpeg",
+          priority: 10,
+          itemName: null,
+          artistName: null,
+          albumName: null,
+          expectedSize: null,
+        },
       });
       expect(downloadId).toBe(123);
     });

src/lib/stores/playbackMode.ts

@@ -73,7 +73,7 @@ function createPlaybackModeStore() {
    * - Polls remote session until track loads
    * - Stops local playback
    */
-  async function transferToRemote(sessionId: string): Promise<void> {
+  async function transferToRemote(sessionId: string | null | undefined): Promise<void> {
     console.log("[PlaybackMode] Transferring to remote session:", sessionId);
     update((s) => ({ ...s, isTransferring: true, transferError: null }));
 
@@ -100,11 +100,11 @@ function createPlaybackModeStore() {
       }
 
       // Update local state
-      sessions.selectSession(sessionId);
+      sessions.selectSession(sessionId ?? null);
       update((s) => ({
         ...s,
         mode: "remote",
-        remoteSessionId: sessionId,
+        remoteSessionId: sessionId ?? null,
         isTransferring: false,
       }));
 

src/lib/stores/sessions.test.ts

@@ -40,8 +40,15 @@ describe("sessions store", () => {
     nowPlayingItem: {
       id: "item-1",
       name: "Test Song",
-      type: "Audio",
-      serverId: "server-1",
+      Type: "Audio",
+      runTimeTicks: null,
+      album: null,
+      albumId: null,
+      albumArtist: null,
+      artists: null,
+      imageTags: null,
+      primaryImageTag: null,
+      albumPrimaryImageTag: null,
     },
     playableMediaTypes: ["Audio", "Video"],
     supportedCommands: ["PlayPause", "Stop", "Seek", "NextTrack", "PreviousTrack"],

src/lib/stores/sessions.ts

@@ -89,7 +89,7 @@ function createSessionsStore() {
   /**
    * Send play/pause toggle command
    */
-  async function sendPlayPause(sessionId: string): Promise<void> {
+  async function sendPlayPause(sessionId: string | null | undefined): Promise<void> {
     try {
       await invoke("remote_send_command", {
         sessionId,
@@ -106,7 +106,7 @@ function createSessionsStore() {
   /**
    * Send stop command
    */
-  async function sendStop(sessionId: string): Promise<void> {
+  async function sendStop(sessionId: string | null | undefined): Promise<void> {
     try {
       await invoke("remote_send_command", {
         sessionId,
@@ -122,7 +122,7 @@ function createSessionsStore() {
   /**
    * Send next track command
    */
-  async function sendNext(sessionId: string): Promise<void> {
+  async function sendNext(sessionId: string | null | undefined): Promise<void> {
     try {
       await invoke("remote_send_command", {
         sessionId,
@@ -138,7 +138,7 @@ function createSessionsStore() {
   /**
    * Send previous track command
    */
-  async function sendPrevious(sessionId: string): Promise<void> {
+  async function sendPrevious(sessionId: string | null | undefined): Promise<void> {
     try {
       await invoke("remote_send_command", {
         sessionId,
@@ -154,7 +154,7 @@ function createSessionsStore() {
   /**
    * Seek to position (in ticks)
    */
-  async function sendSeek(sessionId: string, positionTicks: number): Promise<void> {
+  async function sendSeek(sessionId: string | null | undefined, positionTicks: number): Promise<void> {
     try {
       await invoke("remote_session_seek", {
         sessionId,
@@ -170,7 +170,7 @@ function createSessionsStore() {
   /**
    * Set volume (0-100)
    */
-  async function sendVolume(sessionId: string, volume: number): Promise<void> {
+  async function sendVolume(sessionId: string | null | undefined, volume: number): Promise<void> {
     try {
       await invoke("remote_session_set_volume", {
         sessionId,
@@ -186,7 +186,7 @@ function createSessionsStore() {
   /**
    * Toggle mute
    */
-  async function sendToggleMute(sessionId: string): Promise<void> {
+  async function sendToggleMute(sessionId: string | null | undefined): Promise<void> {
     try {
       await invoke("remote_send_command", {
         sessionId,
@@ -203,7 +203,7 @@ function createSessionsStore() {
    * Play item(s) on remote session
    */
   async function playOnSession(
-    sessionId: string,
+    sessionId: string | null | undefined,
     itemIds: string[],
     startIndex = 0
   ): Promise<void> {