fix(bookplayer): use exported device_find_* API for audio stream lookup

The flashed 0.8.0-dev firmware exports the legacy device_find_by_name /
device_find_first_by_type lookup API, not the newer device_get_* out-param
API. Switching to device_get_* (to match newer SDK headers) caused
'ELF: Can't find symbol device_get_by_name' at load on .129/.114. Revert to
the exported legacy functions, declared locally since the newer SDK header
dropped them. Verified on .129 via serial: elf entry resolves, app shows.

Apps/BookPlayer/main/Source/main.c

@@ -125,14 +125,22 @@ static void play_wav(AppCtx* ctx);
 static void scan_books(AppCtx* ctx);
 
 /* ─── Audio-stream helpers ─── */
+// The flashed firmware exports the legacy device_find_* lookup API; the newer
+// device_get_* (out-param) API is not yet exported on 0.8.0-dev, so calling it
+// fails at load with "missing symbol". The newer SDK headers dropped the legacy
+// declarations, so declare them here (symbols are resolved at runtime by the ELF
+// loader against the flashed firmware).
+extern struct Device* device_find_by_name(const char* name);
+extern struct Device* device_find_first_by_type(const struct DeviceType* type);
+
 static bool find_audio_stream_device(AppCtx* ctx) {
-    struct Device* dev = NULL;
+    struct Device* dev = device_find_by_name("audio-stream");
-    if (device_get_by_name("audio-stream", &dev) == ERROR_NONE && dev) {
+    if (dev) {
         ctx->stream_dev = dev;
         return true;
     }
-    dev = NULL;
+    dev = device_find_first_by_type(&AUDIO_STREAM_TYPE);
-    if (device_get_first_by_type(&AUDIO_STREAM_TYPE, &dev) == ERROR_NONE && dev) {
+    if (dev) {
         ctx->stream_dev = dev;
         return true;
     }