Fix watchdog crashes during file uploads

- Add esp_task_wdt_reset() calls throughout upload path:
  - Before/after SD card file creation (FAT allocation can be slow)
  - Before/after buffer flush writes
  - Every 64 iterations in handleClient loop

- Reduce upload buffer from 8KB to 4KB
  - Keeps individual write times shorter
  - Reduces watchdog risk while maintaining batching benefit

- Switch from time-based to iteration-based handleClient loop
  - More predictable behavior
  - 200 iterations with watchdog resets every 64

src/activities/network/CrossPointWebServerActivity.cpp

@@ -4,6 +4,7 @@
 #include <ESPmDNS.h>
 #include <GfxRenderer.h>
 #include <WiFi.h>
+#include <esp_task_wdt.h>
 #include <qrcode.h>
 
 #include <cstddef>
@@ -316,20 +317,18 @@ void CrossPointWebServerActivity::loop() {
                       timeSinceLastHandleClient);
       }
 
-      // Time-based processing: handle requests for up to 50ms per loop iteration
-      // This is more efficient than a fixed iteration count because:
-      // 1. Processes more data when available (during uploads)
-      // 2. Returns quickly when idle (no wasted spinning)
-      // 3. yield() between calls lets WiFi stack receive more data
-      constexpr unsigned long TIME_BUDGET_MS = 50;
-      const unsigned long handleStart = millis();
-
-      while (webServer->isRunning() && (millis() - handleStart) < TIME_BUDGET_MS) {
+      // Process HTTP requests with watchdog safety
+      // Use iteration-based approach with watchdog resets to prevent crashes
+      // Higher iteration count improves throughput during uploads
+      constexpr int MAX_ITERATIONS = 200;
+      for (int i = 0; i < MAX_ITERATIONS && webServer->isRunning(); i++) {
         webServer->handleClient();
-        // Yield between calls to let WiFi stack process incoming packets
-        // This is critical for throughput - without it, TCP flow control
-        // throttles the sender because our receive buffer fills up
+        // Yield every iteration to let WiFi stack receive more packets
         yield();
+        // Reset watchdog every 50 iterations to prevent timeout during uploads
+        if ((i & 0x3F) == 0) {  // Every 64 iterations
+          esp_task_wdt_reset();
+        }
       }
       lastHandleClientTime = millis();
     }

src/network/CrossPointWebServer.cpp

@@ -304,8 +304,9 @@ static bool uploadSuccess = false;
 static String uploadError = "";
 
 // Upload write buffer - batches small writes into larger SD card operations
-// This improves throughput by reducing the number of SD write syscalls
-constexpr size_t UPLOAD_BUFFER_SIZE = 8192;  // 8KB buffer
+// 4KB is a good balance: large enough to reduce syscall overhead, small enough
+// to keep individual write times short and avoid watchdog issues
+constexpr size_t UPLOAD_BUFFER_SIZE = 4096;  // 4KB buffer
 static uint8_t uploadBuffer[UPLOAD_BUFFER_SIZE];
 static size_t uploadBufferPos = 0;
 
@@ -316,10 +317,12 @@ static size_t writeCount = 0;
 
 static bool flushUploadBuffer() {
   if (uploadBufferPos > 0 && uploadFile) {
+    esp_task_wdt_reset();  // Reset watchdog before potentially slow SD write
     const unsigned long writeStart = millis();
     const size_t written = uploadFile.write(uploadBuffer, uploadBufferPos);
     totalWriteTime += millis() - writeStart;
     writeCount++;
+    esp_task_wdt_reset();  // Reset watchdog after SD write
 
     if (written != uploadBufferPos) {
       Serial.printf("[%lu] [WEB] [UPLOAD] Buffer flush failed: expected %d, wrote %d\n", millis(), uploadBufferPos,
@@ -385,12 +388,14 @@ void CrossPointWebServer::handleUpload() const {
       SdMan.remove(filePath.c_str());
     }
 
-    // Open file for writing
+    // Open file for writing - this can be slow due to FAT cluster allocation
+    esp_task_wdt_reset();
     if (!SdMan.openFileForWrite("WEB", filePath, uploadFile)) {
       uploadError = "Failed to create file on SD card";
       Serial.printf("[%lu] [WEB] [UPLOAD] FAILED to create file: %s\n", millis(), filePath.c_str());
       return;
     }
+    esp_task_wdt_reset();
 
     Serial.printf("[%lu] [WEB] [UPLOAD] File created successfully: %s\n", millis(), filePath.c_str());
   } else if (upload.status == UPLOAD_FILE_WRITE) {