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/battery_estimator.cpp

@@ -0,0 +1,49 @@
+#include "battery_estimator.h"
+
+#include <algorithm>
+
+namespace roro {
+
+namespace {
+struct Point {
+    int millivolts;
+    int percent;
+};
+const Point kCurve[] = {
+    {3270, 0},  {3610, 5},  {3690, 10}, {3710, 15}, {3730, 20}, {3750, 25}, {3770, 30},
+    {3790, 35}, {3800, 40}, {3820, 45}, {3840, 50}, {3850, 55}, {3870, 60}, {3910, 65},
+    {3950, 70}, {3980, 75}, {4020, 80}, {4080, 85}, {4110, 90}, {4150, 95}, {4200, 100},
+};
+const size_t kPoints = sizeof(kCurve) / sizeof(kCurve[0]);
+}  // namespace
+
+int BatteryEstimator::percentFromMillivolts(int mv) {
+    if (mv <= kCurve[0].millivolts) return 0;
+    if (mv >= kCurve[kPoints - 1].millivolts) return 100;
+    for (size_t i = 1; i < kPoints; i++) {
+        if (mv <= kCurve[i].millivolts) {
+            const auto& lo = kCurve[i - 1];
+            const auto& hi = kCurve[i];
+            return lo.percent + (mv - lo.millivolts) * (hi.percent - lo.percent) /
+                                    (hi.millivolts - lo.millivolts);
+        }
+    }
+    return 100;
+}
+
+void BatteryEstimator::addSample(int mv) {
+    samples_[next_] = mv;
+    next_ = (next_ + 1) % kWindow;
+    if (count_ < kWindow) count_++;
+}
+
+int BatteryEstimator::millivolts() const {
+    if (count_ == 0) return 0;
+    // Median: ignores short sags (radio transmit bursts) that would drag an average down.
+    std::array<int, kWindow> sorted = samples_;
+    auto middle = sorted.begin() + count_ / 2;
+    std::nth_element(sorted.begin(), middle, sorted.begin() + count_);
+    return *middle;
+}
+
+}  // namespace roro