feat(DM): instant cache load, manual refresh, full-screen season selector, season persistence fix

- Cache loads synchronously on onShow for instant startup, no auto fetch
- Added manual Refresh button, removed auto refresh that blocked UI
- Made UI non-blocking during fetch (episode list usable while fetching)
- Fixed season loss after player/downloader by preserving season in static s_preserved_season surviving G memset
- Season selector now full-screen overlay parented to lv_scr_act()
- Removed DL Missing batch button and bottom help/status label per UX request
- load_state no longer overwrites browsing season with last_slug season

Apps/DiscoveryMountain/main/Source/storage.c

@@ -151,7 +151,8 @@ void load_state(){
     if(lsn&&cJSON_IsNumber(lsn)) G.cur_season=lsn->valueint;
     if(ls&&cJSON_IsString(ls)){
         strncpy(G.last_slug, ls->valuestring, sizeof(G.last_slug)-1);
-        for(int i=0;i<G.ep_cnt;i++) if(strcmp(G.eps[i].slug,ls->valuestring)==0){ G.cur_ep_idx=i; G.cur_season=G.eps[i].season; break; }
+        // Do NOT overwrite cur_season here based on slug – browsing season is independent
+        // cur_ep_idx will be resolved after cache load in onShow
     }
     cJSON* poss=cJSON_GetObjectItem(r,"positions");
     if(poss && cJSON_IsObject(poss)){