Add Adaptive Polling Intervals to WebServer (#7864)

* feat: add adaptive polling intervals to WebServer

Replace fixed 5ms polling with adaptive intervals based on HTTP activity:
- 50ms during active periods (first 5 seconds after request)
- 200ms during medium activity (5-30 seconds)
- 1000ms during idle periods (30+ seconds)

Reduces CPU usage significantly during idle periods while maintaining
responsiveness when handling HTTP requests.

* Fix integer overflow and magic numbers in WebServer

- Handle millis() overflow in getAdaptiveInterval()
- Replace magic numbers with named constants
- Improve code readability and maintainability

src/mesh/http/WebServer.cpp

@@ -49,6 +49,12 @@ Preferences prefs;
 using namespace httpsserver;
 #include "mesh/http/ContentHandler.h"
 
+static const uint32_t ACTIVE_THRESHOLD_MS = 5000;
+static const uint32_t MEDIUM_THRESHOLD_MS = 30000;
+static const int32_t ACTIVE_INTERVAL_MS = 50;
+static const int32_t MEDIUM_INTERVAL_MS = 200;
+static const int32_t IDLE_INTERVAL_MS = 1000;
+
 static SSLCert *cert;
 static HTTPSServer *secureServer;
 static HTTPServer *insecureServer;
@@ -175,6 +181,32 @@ WebServerThread::WebServerThread() : concurrency::OSThread("WebServer")
     if (!config.network.wifi_enabled && !config.network.eth_enabled) {
         disable();
     }
+    lastActivityTime = millis();
+}
+
+void WebServerThread::markActivity()
+{
+    lastActivityTime = millis();
+}
+
+int32_t WebServerThread::getAdaptiveInterval()
+{
+    uint32_t currentTime = millis();
+    uint32_t timeSinceActivity;
+
+    if (currentTime >= lastActivityTime) {
+        timeSinceActivity = currentTime - lastActivityTime;
+    } else {
+        timeSinceActivity = (UINT32_MAX - lastActivityTime) + currentTime + 1;
+    }
+
+    if (timeSinceActivity < ACTIVE_THRESHOLD_MS) {
+        return ACTIVE_INTERVAL_MS;
+    } else if (timeSinceActivity < MEDIUM_THRESHOLD_MS) {
+        return MEDIUM_INTERVAL_MS;
+    } else {
+        return IDLE_INTERVAL_MS;
+    }
 }
 
 int32_t WebServerThread::runOnce()
@@ -189,8 +221,7 @@ int32_t WebServerThread::runOnce()
         ESP.restart();
     }
 
-    // Loop every 5ms.
-    return (5);
+    return getAdaptiveInterval();
 }
 
 void initWebServer()