firmware: add I2S MEMS microphone driver; fix missing essence migration

Mic: confirmed via its pinout (L/R, WS, SCK, SD, VCC, GND) that the third
target module is a standard I2S digital MEMS mic (INMP441-family). Added
mems_mic.c/h using ESP-IDF's current driver/i2s_std.h API — reports RMS
audio level in dBFS as sensor_type "evp" rather than attempting on-device
voice-band FFT (the browser EVP mode's approach); the backend's existing
statistical anomaly detector handles spike detection from the raw level,
same as it already does for temperature/pressure/presence.

Also fixes a real gap Workstream B's report flagged: User.essence (a live
model column used throughout merged code — /auth/me, inventory purchases,
summon trickle) had no migration line in main.py's lifespan, which would
have broken on the actual production Postgres database.

firmware/esp32p4-sensor-node/main/CMakeLists.txt

@@ -14,6 +14,7 @@ idf_component_register(
         "sensor_registry.c"
         "bmp280.c"
         "rd03e.c"
+        "mems_mic.c"
     INCLUDE_DIRS
         "."
     REQUIRES
@@ -30,8 +31,9 @@ idf_component_register(
 
 # Note (unverified): recent ESP-IDF versions (v5.3+) split the old
 # monolithic "driver" component into per-peripheral components
-# (esp_driver_i2c, esp_driver_uart, ...); "driver" is kept as a
-# backward-compatible umbrella that still pulls those in, which is why a
-# plain REQUIRES driver is used above. If a real build against your exact
-# IDF version complains it can't find driver/i2c_master.h or driver/uart.h,
-# add esp_driver_i2c / esp_driver_uart explicitly to REQUIRES.
+# (esp_driver_i2c, esp_driver_uart, esp_driver_i2s, ...); "driver" is kept
+# as a backward-compatible umbrella that still pulls those in, which is why
+# a plain REQUIRES driver is used above. If a real build against your exact
+# IDF version complains it can't find driver/i2c_master.h, driver/uart.h,
+# or driver/i2s_std.h, add esp_driver_i2c / esp_driver_uart / esp_driver_i2s
+# explicitly to REQUIRES.