touch: widen task-watchdog grace to 20s to stop flash-op WDT reboots (#56)

Decoded coredumps (device + the beta_16 ELFs) are all task-watchdog panics:
CPU0=IDLE0 CPU1=IDLE1, core 0 in spi_flash_op_block_func. A legitimate-but-slow
flash burst (SPIFFS GC, or a bulk DataStore save = thousands of writes) parks both
cores with the cache disabled, starving both IDLE tasks past the ~5s default so the
TWDT panics. The burst can't be chunked under the limit easily and the per-core
WdtHeavyGuard only covers core 0, so re-init the TWDT with a 20s grace (still
catches a genuine multi-second hang) instead. esp_task_wdt_init re-init reconfigures
the running TWDT (old API on this arduino-esp32).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main.cpp

@@ -151,11 +151,23 @@ void halt() {
   unsigned long last_wifi_reconnect_attempt = 0;
 #endif
 
+#include "esp_task_wdt.h"   // task-watchdog reconfigure — see setup() (GH #56)
+
 void setup() {
   Serial.begin(115200);
   delay(200);
   Serial.println("[BOOT] setup start");
 
+  // Widen the task-watchdog grace period. The ~5 s default trips during a legitimate-but-slow flash
+  // burst — a SPIFFS garbage-collect, or a bulk save (DataStore issues ~12 flash ops per contact,
+  // thousands for a full address book). A flash op parks BOTH cores with the cache disabled, so both
+  // IDLE tasks miss their reset and the watchdog panics (decoded coredumps: task_wdt CPU0=IDLE0
+  // CPU1=IDLE1, core 0 in spi_flash_op_block_func). The burst can't be chunked under the limit easily
+  // and the per-core WdtHeavyGuard only covers core 0, so give the dog enough headroom to ride the
+  // burst out while still catching a genuine multi-second hang. (Fixes the random WDT reboots, GH #56.)
+  esp_task_wdt_init(20, true);   // 20 s grace (was ~5 s), keep panic. Re-init reconfigures the
+                                 // already-running TWDT + keeps the idle-task subscriptions.
+
 #if defined(ESP32_PLATFORM) && defined(HAS_TOUCH_UI)
   // Record which slot we booted from so the recovery's "Boot firmware" can return
   // here. Recovery-first itself is enforced by the CUSTOM bootloader (it boots