firmware: fix C6 filesystem provisioning (LittleFS) + ESP-01S env

The C6 never loaded its /config.json, so it fell back to defaults
(SSID RemoteRig, empty password) and couldn't join Wi-Fi. Two bugs:

- Data file was named esp32-config.json but the firmware reads
  /config.json → renamed to config.json.
- Firmware used SPIFFS while pioarduino's uploadfs builds a LittleFS
  image; the SPIFFS mount then reformatted it empty. Switch the C6 to
  LittleFS (matches the toolchain default and the ESP-01S).

Also:
- log loaded ssid/broker/camera_id on config load (not the password)
- platformio.ini: land the ESP-01S env retarget (board d1_mini ->
  esp01_1m, dout, upload_speed 115200) that was missed in 403e1d9
- committed config.json keeps wifi_password blank; the real value is
  flashed to the device, not stored in git

Verified: C6 loads config and associates (got a DHCP lease). MQTT to
the broker is a separate network issue (hub IP / subnet).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

firmware/data/config.json

@@ -0,0 +1,10 @@
+{
+  "wifi_ssid": "RemoteRig",
+  "wifi_password": "",
+  "mqtt_broker": "10.60.1.56",
+  "mqtt_port": 1883,
+  "camera_id": "",
+  "heartbeat_interval_sec": 60,
+  "bat_raw_min": 0,
+  "bat_raw_max": 0
+}