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, 6 insertions, 1 deletions

diff --git a/sdkconfig.defaults b/sdkconfig.defaults
index e612dc8..638f6e8 100644
--- a/sdkconfig.defaults
+++ b/sdkconfig.defaults
@@ -8,7 +8,12 @@ CONFIG_ESPTOOLPY_FLASHSIZE="16MB"
 CONFIG_PARTITION_TABLE_CUSTOM=y
 CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions.csv"
 
-# PSRAM (required for 800x480 framebuffer + JPEG decode)
+# PSRAM (required for 800x480 framebuffer + JPEG decode + local screens).
+# 200 MHz speed is gated behind IDF_EXPERIMENTAL_FEATURES on ESP32-P4 —
+# at the default 20 MHz the DPI bridge underruns continuously trying to
+# feed the panel from PSRAM. 200 MHz gives ~10x more bandwidth and the
+# DPI runs clean.
+CONFIG_IDF_EXPERIMENTAL_FEATURES=y
 CONFIG_SPIRAM=y
 CONFIG_SPIRAM_MODE_HEX=y
 CONFIG_SPIRAM_SPEED_200M=y