Storage: poll the SD card on its own task

A failed mount retries for ~2.5 s, which froze the UI every 15 s while
no card was inserted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/services/storage_service.h

@@ -1,25 +1,34 @@
 #pragma once
 
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+
 #include "service.h"
 #include "storage_monitor.h"
 
 namespace roro {
 
 // Mounts the microSD card (retrying while absent) and feeds its usage to the StorageMonitor.
+// Runs on its own task: a failed mount blocks for seconds and must never stall the UI.
 class StorageService : public Service {
    public:
     explicit StorageService(EventBus& bus) : monitor_(bus) {}
     const char* name() const override { return "storage"; }
-    uint32_t tickIntervalMs() const override { return 15000; }
-    void tick(uint32_t nowMs) override;
+    void start() override;
     void stop() override;
 
-    const StorageState& state() const { return monitor_.state(); }
+    StorageState state() const;
 
    private:
+    static constexpr uint32_t kPollMs = 15000;
+    static void taskEntry(void* self);
+    void poll();
     bool mount();
+
     StorageMonitor monitor_;
     bool mounted_ = false;
+    TaskHandle_t task_ = nullptr;
+    mutable SemaphoreHandle_t lock_ = nullptr;
 };
 
 }  // namespace roro