feat(firmware): ESP32-P4 sensor node — Workstream I core skeleton

New firmware/esp32p4-sensor-node/ ESP-IDF (C, FreeRTOS) project skeleton
per docs/superpowers/specs/2026-07-23-esp32-sensor-node-design.md's
Workstream I:

- Wi-Fi station-mode connect with exponential-backoff reconnect
  (wifi_manager.c), credentials from a gitignored main/device_config.h
  the seeker fills in (template: device_config.h.example).
- Telemetry HTTP client (telemetry_client.c) POSTing the spec's exact
  contract shape to /api/device/telemetry with a Bearer token, via
  esp_http_client + cJSON.
- BME280 I2C driver (bme280.c) with Bosch's public double-precision
  compensation formulas, using ESP-IDF's newer driver/i2c_master.h API.
- LD2410 mmWave presence driver (ld2410.c) over UART, chosen over a
  plain PIR for its distance/motion data richness — its frame-offset
  parsing is flagged as the least-certain code in the firmware.
- sensor_driver_t registry (sensor_driver.h, sensor_registry.c) so new
  sensors are a new driver file + one array line, no main-loop changes.
- README.md: build steps, manual-config walkthrough, wiring/pinouts,
  and an explicit "what's verified vs. not" section plus a real
  hardware caveat (ESP32-P4 has no integrated Wi-Fi radio).

UNVERIFIED AGAINST REAL HARDWARE per the spec's honesty-policy note —
no ESP-IDF toolchain or physical boards available in this environment.
Syntax-checked with gcc against hand-written ESP-IDF API stubs (not
committed) as a best-effort substitute for a real idf.py build.

Workstream J (RTL-SDR experimental module) is explicitly out of scope
here; firmware/esp32p4-sensor-node/components/ is left in place for it.

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

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

@@ -0,0 +1,37 @@
+# Quantumancy sensor node — main component.
+#
+# device_config.h is intentionally NOT listed as a source: it's a header the
+# seeker generates locally (see device_config.h.example + README.md) and is
+# gitignored. If it's missing, the build will fail on the #include in
+# app_main.c with a clear "file not found" — that's deliberate, it's the
+# signal to go copy the example file and fill it in.
+
+idf_component_register(
+    SRCS
+        "app_main.c"
+        "wifi_manager.c"
+        "telemetry_client.c"
+        "sensor_registry.c"
+        "bme280.c"
+        "ld2410.c"
+    INCLUDE_DIRS
+        "."
+    REQUIRES
+        esp_wifi
+        esp_netif
+        esp_event
+        nvs_flash
+        esp_http_client
+        driver
+        json
+        esp_timer
+        log
+)
+
+# 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.