Storage: format the SD card as one FAT32 partition

Repartitions the whole card (f_fdisk + f_mkfs) on the storage task.
Temporarily triggered from the diagnostics screen by typing FORMAT and
Enter; moves to Settings > Storage in step 7.

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

src/services/storage_service.h

@@ -12,21 +12,29 @@ namespace roro {
 // 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) {}
+    explicit StorageService(EventBus& bus) : monitor_(bus), bus_(bus) {}
     const char* name() const override { return "storage"; }
     void start() override;
     void stop() override;
 
     StorageState state() const;
 
+    // Erases the whole card: one partition spanning the card, formatted FAT32. Runs on the storage
+    // task; the result arrives as a Notification. Returns false if a format is already pending.
+    bool requestFormat();
+    bool formatting() const { return formatRequested_; }
+
    private:
     static constexpr uint32_t kPollMs = 15000;
     static void taskEntry(void* self);
     void poll();
     bool mount();
+    void format();
 
     StorageMonitor monitor_;
     bool mounted_ = false;
+    EventBus& bus_;
+    volatile bool formatRequested_ = false;
     TaskHandle_t task_ = nullptr;
     mutable SemaphoreHandle_t lock_ = nullptr;
 };