Fix TWDT starvation, vsync race, and UI responsiveness from review

Three bugs and two UX defects found on review, plus hardening:

- The control loop fed the task watchdog then slept exactly the watchdog
  period (both 10s), tripping the TWDT fractionally late on every single
  iteration. Sleep is now sliced 1s with a reset per slice. Also set
  CONFIG_ESP_TASK_WDT_PANIC=y - the sdkconfig comment claimed a hung task
  panics the chip, but nothing actually made that true.

- The LVGL flush called draw_bitmap (which only queues the framebuffer
  switch) and released LVGL immediately, letting it render the next frame
  into the buffer still being scanned out - the exact PRD 8.2 race the
  double-buffer design exists to prevent. display_present_frame() now
  blocks on a vsync handshake until the swap has latched.

- WiFi reconnect slept up to 30s inside the system event handler, stalling
  all queued WiFi/IP events. Moved to an esp_timer.

- The setpoint label, arc, and mode/room lines rendered the control loop's
  copy of state, which refreshes every 10s - every knob detent looked dead
  for up to 10 seconds. The UI now reads settings live; when the fallback
  ladder clamps the setpoint it shows both values. Room-select focus now
  shows which room is being selected.

- z2m ISO_8601_local timestamps carry a UTC offset the parser ignored,
  which would shift apparent reading age by the local offset (5-6h in the
  US) and permanently trip the fallback ladder. Offset is now honoured.

- Suppressed the cosmetic "control loop stopped" fault in the window
  between relay_init and the control task's first call-in at boot.

- Explicit pullups on the encoder A/B lines.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

main/ui/lvgl_port.c

@@ -36,12 +36,12 @@ static void flush_cb(lv_display_t *disp, const lv_area_t *area, uint8_t *px_map)
     (void)area;
 
     /*
-     * px_map is one of the panel's own framebuffers, so this does not copy —
-     * the RGB driver just switches which buffer is being scanned out and waits
-     * for the switch to take effect.
+     * px_map is one of the panel's own framebuffers, so no copy happens — the
+     * RGB driver switches which buffer is scanned out. present_frame blocks
+     * until that switch has latched at vsync; releasing LVGL any earlier would
+     * let it render the next frame into the buffer still on screen.
      */
-    esp_lcd_panel_handle_t panel = display_panel();
-    esp_lcd_panel_draw_bitmap(panel, 0, 0, DISPLAY_H_RES, DISPLAY_V_RES, px_map);
+    display_present_frame(px_map);
 
     lv_display_flush_ready(disp);
 }