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/platform/nvs_store.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <Preferences.h>
+
+#include "key_value_store.h"
+
+namespace roro {
+
+// Settings persistence in the ESP32's internal flash (NVS).
+class NvsStore : public KeyValueStore {
+   public:
+    void begin() { prefs_.begin("roro", false); }
+
+    bool getInt(const char* key, int32_t& out) override {
+        if (!prefs_.isKey(key)) return false;
+        out = prefs_.getInt(key);
+        return true;
+    }
+    bool getString(const char* key, std::string& out) override {
+        if (!prefs_.isKey(key)) return false;
+        out = prefs_.getString(key).c_str();
+        return true;
+    }
+    void putInt(const char* key, int32_t value) override { prefs_.putInt(key, value); }
+    void putString(const char* key, const std::string& value) override {
+        prefs_.putString(key, value.c_str());
+    }
+
+   private:
+    Preferences prefs_;
+};
+
+}  // namespace roro