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, 3 insertions, 1 deletions

diff --git a/main/viewport_state.c b/main/viewport_state.c
index 9115ce3..3ae8f81 100644
--- a/main/viewport_state.c
+++ b/main/viewport_state.c
@@ -13,7 +13,9 @@ void viewport_state_init(void)
 {
     memset(&s_state, 0, sizeof(s_state));
     s_state.configured      = false;
-    s_state.state           = VIEWPORT_STATE_UNCONFIGURED;
+    // State is always AWAKE or ASLEEP. UNCONFIGURED is reported via the
+    // `configured` flag, not as a state value. Boot is always asleep.
+    s_state.state           = VIEWPORT_STATE_ASLEEP;
     s_state.brightness      = 80;
     s_state.idle_timeout_ms = 60000;
     s_state.orientation     = VIEWPORT_ORIENTATION_PORTRAIT;