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/network.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "app_context.h"
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+uint16_t my_htons(uint16_t v);
+bool resolve_host(const char* host, uint32_t* out_ip);
+void normalize_audio_url(const char* in, char* out, size_t out_len);
+
+// Robust HTTP GET with PSRAM buffer, returns length and allocates *out_body (must be free'd via free/heap_caps_free)
+int http_get_raw(const char* url, char** out_body);
+
+// Fetch seasons and episodes from PB
+void fetch_data(void);
+
+#ifdef __cplusplus
+}
+#endif