feat: persist pressure history to LittleFS across reboots

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

WeatherPredictor/history.cpp

@@ -1,3 +1,4 @@
+#include <LittleFS.h>
 #include "config.h"
 #include "history.h"
 
@@ -36,3 +37,35 @@ bool historyTrendDelta(float& outDelta) {
   outDelta = latest.mslHpa - past.mslHpa;
   return true;
 }
+
+static const char* HPATH = "/history.dat";
+
+// Binary format: [int32 count][count * Sample], stored oldest-first.
+bool historySave() {
+  File f = LittleFS.open(HPATH, "w");
+  if (!f) return false;
+  int32_t n = s_count;
+  f.write((const uint8_t*)&n, sizeof(n));
+  for (int i = 0; i < s_count; i++) {
+    Sample s = historyGet(i);
+    f.write((const uint8_t*)&s, sizeof(s));
+  }
+  f.close();
+  return true;
+}
+
+bool historyLoad() {
+  File f = LittleFS.open(HPATH, "r");
+  if (!f) return false;
+  int32_t n = 0;
+  if (f.read((uint8_t*)&n, sizeof(n)) != sizeof(n)) { f.close(); return false; }
+  if (n < 0 || n > HISTORY_SIZE) { f.close(); return false; }
+  s_head = 0; s_count = 0;
+  for (int i = 0; i < n; i++) {
+    Sample s;
+    if (f.read((uint8_t*)&s, sizeof(s)) != sizeof(s)) break;
+    historyAdd(s.epoch, s.mslHpa, s.tempC);
+  }
+  f.close();
+  return true;
+}