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.cpp

@@ -1,6 +1,10 @@
 #include "storage_service.h"
 
 #include <SD.h>
+#include <ff.h>
+#include <sd_diskio.h>
+
+#include <memory>
 
 #include "platform/pins.h"
 #include "platform/shared_spi.h"
@@ -31,11 +35,43 @@ StorageState StorageService::state() const {
 void StorageService::taskEntry(void* self) {
     auto* service = static_cast<StorageService*>(self);
     for (;;) {
+        if (service->formatRequested_) {
+            service->format();
+            service->formatRequested_ = false;
+        }
         service->poll();
-        vTaskDelay(pdMS_TO_TICKS(kPollMs));
+        // Sleep until the next poll, or until a format request wakes us early.
+        ulTaskNotifyTake(pdTRUE, pdMS_TO_TICKS(kPollMs));
     }
 }
 
+bool StorageService::requestFormat() {
+    if (formatRequested_ || !task_) return false;
+    formatRequested_ = true;
+    xTaskNotifyGive(task_);
+    return true;
+}
+
+void StorageService::format() {
+    if (mounted_) SD.end();
+    mounted_ = false;
+
+    bool ok = false;
+    uint8_t pdrv = sdcard_init(pins::kSdCs, &sharedSpi(), 20000000);
+    if (pdrv != 0xFF) {
+        constexpr size_t kWorkSize = 4096;  // FF_MAX_SS
+        std::unique_ptr<uint8_t[]> work(new uint8_t[kWorkSize]);
+        LBA_t partitions[] = {100, 0};  // one partition, 100 % of the card
+        char drive[3] = {static_cast<char>('0' + pdrv), ':', 0};
+        MKFS_PARM options = {FM_FAT32, 0, 0, 0, 0};
+        ok = f_fdisk(pdrv, partitions, work.get()) == FR_OK &&
+             f_mkfs(drive, &options, work.get(), kWorkSize) == FR_OK;
+        sdcard_uninit(pdrv);
+    }
+    bus_.publish(Event::withText(EventType::Notification, ok ? "SD card formatted" : "SD card format failed",
+                                 static_cast<int32_t>(ok ? NotificationLevel::Info : NotificationLevel::Warning)));
+}
+
 bool StorageService::mount() {
     return SD.begin(pins::kSdCs, sharedSpi(), 20000000, "/sd", 5, false);
 }