feat(DM+SdDDL): sequential full-season download queue, fix close crash, return true

- DM: add dl_missing_* fields to AppCtx for sequential queue
- DM player: count_missing_in_season, find_next_missing, download_episode, download_missing_season_start/next
- DM main onResult: auto-continue queue when dl_missing_active, updates status DL X/Y, finishes with done ok/fail
- SdDownloader: file exists returns true (Already on SD) with total=file size, not false
- SdDownloader: set_result_and_close minimal bundle (only success bool) to avoid internal heap OOM crash on close
- SdDownloader: Cancel button becomes Close after done, calls tt_app_stop() directly (manual close per request, auto-close unreliable)
- Fixes crash on close observed in demo mode (file exists) and after download done

Tested on 192.168.68.133: SdDownloader shows Already on SD + Close, DM shows S10 5/6 after sequential, no crash on open/close cycles

Apps/DiscoveryMountain/main/Source/player.c

@@ -62,24 +62,81 @@ static bool try_external_downloader(int idx) {
     return true;
 }
 
-static bool try_external_downloader_batch(int season) {
-    // Reverted to single-file mode – batch array caused crashes in SdDownloader
-    // Now just download first missing episode in season
-    int first_missing = -1;
+int count_missing_in_season(int season){
+    int cnt=0;
     for(int i=0;i<G.ep_cnt;i++){
-        if(G.eps[i].season == season && !G.eps[i].seen && strlen(G.eps[i].audio_url)>=8){
-            first_missing = i;
-            break;
-        }
+        if(G.eps[i].season==season && !G.eps[i].seen && strlen(G.eps[i].audio_url)>=8) cnt++;
     }
-    if(first_missing==-1){
+    return cnt;
+}
+int find_next_missing_in_season(int season){
+    for(int i=0;i<G.ep_cnt;i++){
+        if(G.eps[i].season==season && !G.eps[i].seen && strlen(G.eps[i].audio_url)>=8) return i;
+    }
+    return -1;
+}
+bool download_episode(int idx){
+    return try_external_downloader(idx);
+}
+bool download_missing_next(void){
+    if(!G.dl_missing_active) return false;
+    int next = find_next_missing_in_season(G.dl_missing_season);
+    if(next==-1){
+        // No more missing – done
+        G.dl_missing_active=false;
+        tt_lvgl_lock(portMAX_DELAY);
+        if(G.lbl_status){
+            char msg[64];
+            snprintf(msg,sizeof(msg),"DL S%02d done %d ok %d fail", G.dl_missing_season, G.dl_missing_done, G.dl_missing_failed);
+            lv_label_set_text(G.lbl_status, msg);
+        }
+        tt_lvgl_unlock();
+        return false;
+    }
+    // Update UI for next file
+    tt_lvgl_lock(portMAX_DELAY);
+    if(G.lbl_status){
+        char msg[64];
+        snprintf(msg,sizeof(msg),"DL %d/%d S%02d...", G.dl_missing_done+1, G.dl_missing_total, G.dl_missing_season);
+        lv_label_set_text(G.lbl_status, msg);
+    }
+    tt_lvgl_unlock();
+    return try_external_downloader(next);
+}
+bool download_missing_season_start(int season){
+    int missing = count_missing_in_season(season);
+    if(missing==0){
         tt_lvgl_lock(portMAX_DELAY);
         if(G.lbl_status) lv_label_set_text(G.lbl_status,"Season already cached");
         tt_lvgl_unlock();
+        G.dl_missing_active=false;
         return true;
     }
-    ESP_LOGI(TAG, "DL Missing (single-file revert) – downloading first missing S%02d idx %d", season, first_missing);
-    return try_external_downloader(first_missing);
+    ESP_LOGI(TAG, "Starting sequential DL for S%02d, %d missing", season, missing);
+    G.dl_missing_active=true;
+    G.dl_missing_season=season;
+    G.dl_missing_total=missing;
+    G.dl_missing_done=0;
+    G.dl_missing_failed=0;
+    int first = find_next_missing_in_season(season);
+    if(first==-1){
+        G.dl_missing_active=false;
+        return true;
+    }
+    // Update status
+    tt_lvgl_lock(portMAX_DELAY);
+    if(G.lbl_status){
+        char msg[64];
+        snprintf(msg,sizeof(msg),"DL 1/%d S%02d...", missing, season);
+        lv_label_set_text(G.lbl_status, msg);
+    }
+    tt_lvgl_unlock();
+    return try_external_downloader(first);
+}
+
+static bool try_external_downloader_batch(int season) {
+    // Sequential queue – safe single-file mode
+    return download_missing_season_start(season);
 }
 
 void start_idx_internal(int idx){