Add M0 services: settings, battery, clock, storage, power

lib/services holds the host-tested logic:
- Settings: typed, validated, persisted, SettingChanged events,
  transmit gated on a confirmed Region
- BatteryEstimator: LiPo curve, median smoothing against TX sags
- ClockModel: source priority GNSS > NTP > mesh, relative ages,
  Europe/Brussels local time via POSIX TZ
- StorageMonitor: warning once per boot at 80%, Logs stop at 90%,
  Captures stop with < 2 MiB left
- PowerPolicy / PowerButton: dim/off timeouts, wake key swallowed only
  when the screen was off, G0 long press

src/services wires them to the hardware (NVS, battery ADC, SD on the
shared SPI bus with the LoRa CS held high, backlight, deep sleep), and
main.cpp is a temporary diagnostics screen for the hardware checks.

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

src/services/storage_service.cpp

@@ -0,0 +1,36 @@
+#include "storage_service.h"
+
+#include <SD.h>
+
+#include "platform/pins.h"
+#include "platform/shared_spi.h"
+
+namespace roro {
+
+bool StorageService::mount() {
+    return SD.begin(pins::kSdCs, sharedSpi(), 20000000, "/sd", 5, false);
+}
+
+void StorageService::tick(uint32_t) {
+    if (mounted_) {
+        // Detect removal: the root can no longer be opened.
+        File root = SD.open("/");
+        if (!root) {
+            SD.end();
+            mounted_ = false;
+        }
+    }
+    if (!mounted_) mounted_ = mount();
+
+    if (mounted_)
+        monitor_.update(true, SD.totalBytes(), SD.usedBytes());
+    else
+        monitor_.update(false, 0, 0);
+}
+
+void StorageService::stop() {
+    if (mounted_) SD.end();
+    mounted_ = false;
+}
+
+}  // namespace roro