M3 WIP: DSI bring-up + state machine + identity overlay

DSI / panel:
- LDO_VO3 acquired at 2500 mV (VDD_MIPI_DPHY) — without this the PHY
  PLL busy-waits forever inside esp_lcd_new_dsi_bus.
- PSRAM bumped to 200 MHz (CONFIG_IDF_EXPERIMENTAL_FEATURES) to keep
  the DPI fed without underruns.
- Pi-7"-style 800x480 panel init (REG_POWERON, PORTA/PORTB/PWM/PORTC)
  + 16-bit RGB565 framebuffer with portrait-mode rotation buffer in
  PSRAM. Currently shows garbled output — known issue, next commit
  switches to the TC358762-bridge-aware init sequence.

State + UX:
- viewport_state simplified to AWAKE/ASLEEP only; "unconfigured" is
  a flag, not a state. Tap always toggles; content choice (identity
  vs frame) is driven by the configured flag.
- BOOT button arms a 15 s identity overlay via local_screens_overlay;
  expired callback returns to prior state.
- Boot-done indicator: two backlight flashes (no usable LED GPIO on
  the Waveshare board — GPIO 35 BOOT is shared with EMAC TXD1).
- Best-effort subsystem init in app_main; display init deferred to
  its own task so a panel hang can't block networking.

Display test pattern: solid R/G/B for 2 s each on boot to characterize
the garble independent of text rendering.

1 files changed, 2 insertions, 25 deletions

diff --git a/main/button.c b/main/button.c
index 9ac34a1..26e7cff 100644
--- a/main/button.c
+++ b/main/button.c
@@ -25,28 +25,11 @@ static const char *TAG = "button";
 #define LONG_HOLD_MS         5000
 #define OVERLAY_MS           15000
 
-static esp_timer_handle_t s_overlay_timer;
-
-static void overlay_expired(void *arg)
-{
-    if (display_is_up()) {
-        local_screens_restore_for_state();
-        // Caller (state_machine_set) had backlight off if asleep — the
-        // overlay turned it on. Force it back off if we're asleep.
-        // Easiest: re-issue display_sleep, the wake_then_sleep path is
-        // owned by the state machine.
-    }
-    ESP_LOGI(TAG, "IP overlay expired");
-}
-
 static void start_overlay(void)
 {
     if (!display_is_up()) return;
-    esp_timer_stop(s_overlay_timer);
-    display_wake();  // turn backlight on in case we were asleep
-    local_screens_show_ip();
-    esp_timer_start_once(s_overlay_timer, (uint64_t)OVERLAY_MS * 1000ULL);
-    ESP_LOGI(TAG, "BOOT short-press → IP overlay for %dms", OVERLAY_MS);
+    local_screens_overlay(OVERLAY_MS);
+    ESP_LOGI(TAG, "BOOT short-press → identity overlay for %dms", OVERLAY_MS);
 }
 
 static void factory_reset(void)
@@ -104,12 +87,6 @@ esp_err_t button_init(void)
         return err;
     }
 
-    esp_timer_create_args_t targs = {
-        .callback = &overlay_expired,
-        .name     = "boot_overlay",
-    };
-    esp_timer_create(&targs, &s_overlay_timer);
-
     BaseType_t ok = xTaskCreate(button_task, "boot_btn", 3072, NULL, 3, NULL);
     if (ok != pdPASS) return ESP_FAIL;