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.h

@@ -10,13 +10,17 @@ void createSSLCert();
 
 class WebServerThread : private concurrency::OSThread
 {
+  private:
+    uint32_t lastActivityTime = 0;
 
   public:
     WebServerThread();
     uint32_t requestRestart = 0;
+    void markActivity();
 
   protected:
     virtual int32_t runOnce() override;
+    int32_t getAdaptiveInterval();
 };
 
 extern WebServerThread *webServerThread;