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

lib/services/src/storage_monitor.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <cstdint>
+
+#include "event_bus.h"
+
+namespace roro {
+
+struct StorageState {
+    bool present = false;
+    uint64_t totalBytes = 0;
+    uint64_t usedBytes = 0;
+    int usedPercent = 0;
+    int level = 0;  // 0, 80, 90 or 100 (full)
+    bool logsAllowed = false;
+    bool capturesAllowed = false;
+};
+
+// Applies the SD card rules (see CONTEXT.md): Storage Warning once per boot past 80 %, Logs stop
+// past 90 % to keep room for Captures, Captures stop when the card is full.
+class StorageMonitor {
+   public:
+    static constexpr uint64_t kFullReserveBytes = 2ull * 1024 * 1024;
+
+    explicit StorageMonitor(EventBus& bus) : bus_(bus) {}
+
+    void update(bool present, uint64_t totalBytes, uint64_t usedBytes);
+    const StorageState& state() const { return state_; }
+
+   private:
+    EventBus& bus_;
+    StorageState state_;
+    bool warned_ = false;
+};
+
+}  // namespace roro