Add maintenance API endpoints

docs/API.md

@@ -26,11 +26,15 @@ Current firmware version:
 
 ```text
 GET  /
+GET  /api/v1/health
+GET  /api/v1/capabilities
 GET  /api/v1/status
 GET  /api/v1/config
+GET  /api/v1/config/export
 
 POST /api/v1/relay/set
 
+POST /api/v1/config/import
 POST /api/v1/config/device
 POST /api/v1/config/relay
 POST /api/v1/config/temp
@@ -75,6 +79,70 @@ POST /api/v1/relay/set
 
 The dashboard is a client only. It may cache last-known values for display, but the Cargo ESP32 remains the source of truth for relay state, BMS state, alarms, and configuration.
 
+## Health
+
+### GET /api/v1/health
+
+Returns a lightweight liveness response for dashboards and service tools.
+
+```json
+{
+  "type": "health_response",
+  "ok": true,
+  "api_version": "v1",
+  "firmware_name": "overland-controller",
+  "firmware_version": "0.4.0",
+  "uptime_seconds": 123,
+  "network": {
+    "ap_enabled": true,
+    "ap_ip": "192.168.4.1",
+    "sta_enabled": true,
+    "sta_connected": false,
+    "sta_ssid": "",
+    "sta_ip": ""
+  },
+  "bms": {
+    "configured": true,
+    "connected": false
+  }
+}
+```
+
+## Capabilities
+
+### GET /api/v1/capabilities
+
+Returns API and feature discovery data for clients.
+
+```json
+{
+  "type": "capabilities_response",
+  "ok": true,
+  "api_version": "v1",
+  "firmware_name": "overland-controller",
+  "firmware_version": "0.4.0",
+  "endpoints": [
+    "GET /api/v1/status",
+    "POST /api/v1/relay/set"
+  ],
+  "limits": {
+    "relay_count": 2,
+    "temperature_sensor_count": 8,
+    "runtime_temperature_status_count": 4,
+    "wifi_network_count": 3
+  },
+  "features": {
+    "relay_control": true,
+    "temperature_scan": true,
+    "wifi_config": true,
+    "config_backup_restore": true,
+    "bms_setup": true,
+    "uart_json": true,
+    "root_compatibility_aliases": true
+  }
+}
+```
+
 ## Status
 
 ### GET /api/v1/status
@@ -261,19 +329,19 @@ Returns saved controller configuration.
     "address": "AA:BB:CC:DD:EE:FF",
     "address_type": "public"
   },
+  "temperature_sensor_count": 4,
   "temperature_sensors": [
     {
       "id": "temp_1",
       "name": "Cabin",
       "address": "28:AA:BB:CC:DD:EE:FF:00",
-      "enabled": true
+      "enabled": true,
+      "weather": false
     }
   ]
 }
 ```
 
-Note: current `GET /api/v1/config` omits the `weather` field, while `/api/v1/status.config.temperature_sensors[]` includes it.
-
 ### POST /api/v1/config/device
 
 Updates the controller display name.
@@ -368,6 +436,63 @@ Clears saved configuration and restores firmware defaults.
 
 Returns the reset config.
 
+### GET /api/v1/config/export
+
+Returns a backup envelope containing controller config and saved WiFi networks.
+
+Important: export includes saved WiFi passwords so the backup can be restored. Treat the response as sensitive.
+
+```json
+{
+  "type": "config_export_response",
+  "ok": true,
+  "api_version": "v1",
+  "firmware_name": "overland-controller",
+  "firmware_version": "0.4.0",
+  "config": {
+    "device_name": "Overland Controller",
+    "temperature_sensor_count": 4,
+    "relays": [],
+    "bms": {},
+    "temperature_sensors": []
+  },
+  "wifi": {
+    "networks": [
+      {
+        "index": 1,
+        "ssid": "Starlink",
+        "priority": 1,
+        "password_set": true,
+        "password": "password_here"
+      }
+    ]
+  }
+}
+```
+
+### POST /api/v1/config/import
+
+Restores a config backup. The preferred request shape is the same envelope returned by `GET /api/v1/config/export`.
+
+```json
+{
+  "config": {
+    "device_name": "Overland Controller",
+    "temperature_sensor_count": 4,
+    "relays": [],
+    "bms": {},
+    "temperature_sensors": []
+  },
+  "wifi": {
+    "networks": []
+  }
+}
+```
+
+The endpoint also accepts the bare config object without an outer `config` field. When `wifi.networks` is included, saved STA WiFi networks are replaced and persisted. It does not initiate STA reconnect; use `POST /api/v1/wifi/connect` after import if needed.
+
+Returns the updated config.
+
 ## Relay Control
 
 ### POST /api/v1/relay/set
@@ -671,6 +796,7 @@ Known error codes:
 
 ```text
 invalid_json
+invalid_config
 unknown_relay
 unknown_temp_sensor
 invalid_temp_selection