main: code-review fixes — brightness units, OTA stall cap, stats + locking

- display: s_last_pwm cached the raw 0-100 percentage at init but
  display_wake writes it straight to REG_PWM (0-255 duty) — first wake
  ran visibly dim until a /config brightness change. Shared pct_to_duty
  helper now converts in both paths.
- http_api: cap consecutive OTA recv timeouts (a stalled client spun
  forever holding s_ota_in_progress, wedging OTA until reboot); cap
  viewport name at 54 chars so viewport-<name> fits the 63-byte mDNS
  label; log mdns_service_refresh failures; /state builds JSON from a
  snapshot instead of holding the state lock across ~25 cJSON allocs;
  respond_400 delegates to respond_status.
- stream_server: bytes_in_window now counts painted frames only (frames
  discarded while asleep inflated the first post-wake window's MB/s,
  avg-jpeg and chunk/wire averages; recv_bytes folded in); so_rcvbuf
  carried into the stats snapshot under the mux; drop dead HEADER_BYTES;
  merge read_body_instrumented into read_n.
- state_machine: transition mutex serializes concurrent wake/sleep
  (display side-effects ran after the state lock dropped, so racing
  callers could leave the backlight contradicting st->state); wake-path
  placeholder paint now takes the decoder lock like the stream path
  (concurrent esp_lcd_panel_draw_bitmap from two tasks isn't safe).
- local_screens: overlay paint takes the decoder lock too; check the
  overlay timer create; panel dims from viewport_state.h.
- jpeg_decoder: try_lock before init returns busy instead of passing a
  NULL semaphore to xSemaphoreTake.
- net_eth: clear cached IP string on link down (stale /state + info).
- dead code: display_present_bgr888, TOUCH_FT5426_ADDR, touch s_task,
  JPEG_DECODER_MAX_OUTPUT_BYTES; doc drift in nvs_config.h /
  jpeg_decoder.h / app_main flag legend.

1 files changed, 12 insertions, 3 deletions

diff --git a/main/local_screens.c b/main/local_screens.c
index 1277d00..351c7c5 100644
--- a/main/local_screens.c
+++ b/main/local_screens.c
@@ -9,13 +9,14 @@
 
 #include "chip_temp.h"
 #include "display.h"
+#include "jpeg_decoder.h"
 #include "net_eth.h"
 #include "viewport_state.h"
 
 static const char *TAG = "screens";
 
-#define PANEL_W      800
-#define PANEL_H      480
+#define PANEL_W      VIEWPORT_PANEL_WIDTH
+#define PANEL_H      VIEWPORT_PANEL_HEIGHT
 #define MAX_BUF_PX   (PANEL_W * PANEL_H)
 
 // 8x8 bitmap font, lit pixels = foreground. Covers the characters used by
@@ -150,7 +151,11 @@ esp_err_t local_screens_init(void)
         .callback = &overlay_expired_cb,
         .name     = "info_overlay",
     };
-    esp_timer_create(&args, &s_overlay_timer);
+    esp_err_t err = esp_timer_create(&args, &s_overlay_timer);
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "overlay timer create failed: %s", esp_err_to_name(err));
+        return err;
+    }
     return ESP_OK;
 }
 
@@ -174,7 +179,11 @@ esp_err_t local_screens_overlay(uint32_t duration_ms)
     if (!display_is_up()) return ESP_ERR_INVALID_STATE;
     esp_timer_stop(s_overlay_timer);
     display_wake();
+    // Serialize the overlay paint against the stream decode-task's paints
+    // (concurrent esp_lcd_panel_draw_bitmap calls aren't safe).
+    if (!jpeg_decoder_try_lock(500)) return ESP_ERR_TIMEOUT;
     esp_err_t err = local_screens_show_info();
+    jpeg_decoder_unlock();
     if (err != ESP_OK) return err;
     s_overlay_active = true;
     return esp_timer_start_once(s_overlay_timer,