refactor(DiscoveryMountain): split monolithic main.c into modular files

- Extracted app_context (global AppCtx G definition)
- storage: path helpers, LRU, sort, fmt_time, per-episode resume map, state persistence
- network: resolve_host, normalize URL, http_get_raw with growing PSRAM buffer, fetch_data
- download: dl_ep_raw with progress tracking, cancel, overlay UI (show/hide/update)
- player: audio device, stream, play_task with resume seek, start/select/next/prev with position save/restore
- ui: build_ui, timers, season picker, button callbacks, periodic save
- main: minimal glue, fetch_task, onShow/onHide, app registration
- Preserves all previous fixes: download progress overlay, per-episode resume, robust download handling
- Build verified: 111 undef, all exported

Apps/DiscoveryMountain/main/Source/download.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "app_context.h"
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Raw download to file with progress tracking
+bool dl_ep_raw(EpInfo* ep);
+bool dl_ep(EpInfo* ep);
+
+// Download task
+void dl_task(void* arg);
+
+// Download overlay UI
+void hide_dl_overlay(void);
+void show_dl_overlay_locked(const char* ep_title, const char* slug, int season, int ep_num);
+void update_dl_overlay_ui(void);
+
+#ifdef __cplusplus
+}
+#endif