feat(web): scrollable Forecast log with fixed height

Cap the log panel at ~216px with a thin themed scrollbar so a long
forecast history does not stretch the page.

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

WeatherPredictor/WeatherPredictor.ino

@@ -88,6 +88,15 @@ void loop() {
     tSample = now;
     sampleNow();
     displayRender(g_state);
+    Serial.printf("heap=%u maxblock=%u\n", ESP.getFreeHeap(), ESP.getMaxFreeBlockSize());
+    // Safety net: if the largest contiguous block gets too small, the TCP stack
+    // can no longer send responses. Persist and reboot to defragment.
+    if (ESP.getMaxFreeBlockSize() < 6000) {
+      Serial.println(F("Low memory -> saving history and restarting"));
+      historySave();
+      delay(50);
+      ESP.restart();
+    }
   }
 
   if (now - tHistory >= HISTORY_INTERVAL_MS) {

WeatherPredictor/web_page.h

@@ -103,7 +103,11 @@ static const char INDEX_HTML[] PROGMEM = R"HTML(
   .cap{color:var(--muted); font-size:.74rem; letter-spacing:.06em}
 
   /* Forecast log */
-  .log{list-style:none; margin:2px 0 0; padding:0}
+  .log{list-style:none; margin:2px 0 0; padding:0 8px 0 0; max-height:216px; overflow-y:auto;
+       scrollbar-width:thin; scrollbar-color:var(--line) transparent}
+  .log::-webkit-scrollbar{width:8px}
+  .log::-webkit-scrollbar-thumb{background:var(--line); border-radius:8px}
+  .log::-webkit-scrollbar-track{background:transparent}
   .log li{display:flex; align-items:center; gap:13px; padding:12px 0; border-top:1px solid var(--line)}
   .log li:first-child{border-top:0}
   .log .dot{width:9px; height:9px; border-radius:50%; flex:0 0 auto}

WeatherPredictor/web_server.cpp

@@ -27,41 +27,44 @@ static void handleCurrent() {
   doc["haveTrend"] = g_state.haveTrend;
   doc["forecast"]  = g_state.haveTrend ? g_state.forecast.text : "Collecting data...";
   doc["category"]  = g_state.haveTrend ? categoryShort(g_state.forecast.category) : "...";
+  doc["heap"]      = ESP.getFreeHeap();       // for monitoring memory health
   String out;
   serializeJson(doc, out);
   server.send(200, "application/json", out);
 }
 
+// Streamed (chunked) so we never build a large String/JsonDocument on the heap.
 static void handleHistory() {
-  JsonDocument doc;
-  JsonArray arr = doc.to<JsonArray>();
+  server.setContentLength(CONTENT_LENGTH_UNKNOWN);
+  server.send(200, "application/json", "");
+  server.sendContent("[");
+  char buf[80];
   int n = historyCount();
   for (int i = 0; i < n; i++) {
     Sample s = historyGet(i);
-    JsonObject o = arr.add<JsonObject>();
-    o["t"]    = s.epoch;
-    o["msl"]  = s.mslHpa;
-    o["temp"] = s.tempC;
+    snprintf(buf, sizeof(buf), "%s{\"t\":%lu,\"msl\":%.1f,\"temp\":%.1f}",
+             i ? "," : "", (unsigned long)s.epoch, s.mslHpa, s.tempC);
+    server.sendContent(buf);
   }
-  String out;
-  serializeJson(doc, out);
-  server.send(200, "application/json", out);
+  server.sendContent("]");
 }
 
+// Streamed (chunked). Forecast phrases contain no quotes/backslashes, so they
+// are safe to embed directly in JSON.
 static void handleForecasts() {
-  JsonDocument doc;
-  JsonArray arr = doc.to<JsonArray>();
+  server.setContentLength(CONTENT_LENGTH_UNKNOWN);
+  server.send(200, "application/json", "");
+  server.sendContent("[");
+  char buf[128];
   int n = flogCount();
-  for (int i = n - 1; i >= 0; i--) {          // newest first
+  for (int i = n - 1, first = 1; i >= 0; i--, first = 0) {   // newest first
     FcastEntry e = flogGet(i);
-    JsonObject o = arr.add<JsonObject>();
-    o["t"]    = e.epoch;
-    o["cat"]  = categoryShort((WxCategory)e.cat);
-    o["text"] = forecastTextForLetter(e.letter);
+    snprintf(buf, sizeof(buf), "%s{\"t\":%lu,\"cat\":\"%s\",\"text\":\"%s\"}",
+             first ? "" : ",", (unsigned long)e.epoch,
+             categoryShort((WxCategory)e.cat), forecastTextForLetter(e.letter));
+    server.sendContent(buf);
   }
-  String out;
-  serializeJson(doc, out);
-  server.send(200, "application/json", out);
+  server.sendContent("]");
 }
 
 static void handleGetSettings() {