First successful flash: placeholder face live; fix 20MHz PSRAM trap; power ladder

- firmware boots to a rendered LVGL face in 1.57s (eyes + smile + tag)
- sdkconfig: CONFIG_IDF_EXPERIMENTAL_FEATURES=y unlocks SPIRAM 200MHz
  (silently degraded to 20MHz before -> MIPI-DSI underrun -> LVGL lock
  starvation -> task watchdog); mirrors official 08_lvgl_demo_v9 config
- architecture.md: power management section (user prime concern) —
  active/ambient/dormant/night ladder, levers, hard edges, <=300ms wake
- AGENTS/CLAUDE: replace stale bring-up warnings with verified commands

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

firmware/sdkconfig.defaults

@@ -5,10 +5,19 @@ CONFIG_IDF_TARGET="esp32p4"
 CONFIG_ESPTOOLPY_FLASHSIZE_32MB=y
 CONFIG_PARTITION_TABLE_SINGLE_APP_LARGE=y
 
-# 32 MB in-package PSRAM (hex mode) — LVGL frame buffers live here
+# PSRAM at 200 MHz — REQUIRED for the 800x800 MIPI-DSI framebuffer.
+# 200 MHz is gated behind IDF_EXPERIMENTAL_FEATURES; without it the build
+# silently falls back to 20 MHz and the DSI underruns (mirrors the official
+# 08_lvgl_demo_v9 example config).
 CONFIG_SPIRAM=y
-CONFIG_SPIRAM_MODE_HEX=y
+CONFIG_IDF_EXPERIMENTAL_FEATURES=y
 CONFIG_SPIRAM_SPEED_200M=y
+CONFIG_SPIRAM_XIP_FROM_PSRAM=y
+CONFIG_CACHE_L2_CACHE_256KB=y
+CONFIG_CACHE_L2_CACHE_LINE_128B=y
 
 CONFIG_COMPILER_OPTIMIZATION_PERF=y
 CONFIG_FREERTOS_HZ=1000
+
+# LVGL font for the bring-up placeholder face
+CONFIG_LV_FONT_MONTSERRAT_48=y