redbear-power: add load average to JSON export

Add a JsonLoad struct with load_avg_1m/5m/15m fields and include it in the --json snapshot. Values are read from app.load_avg. Build, 224 tests, clippy, and fmt clean.

local/recipes/system/redbear-power/source/src/render.rs

@@ -2493,6 +2493,7 @@ pub fn render_json(app: &App) -> io::Result<()> {
         cpu: JsonCpu,
         memory: JsonMemory,
         power: JsonPower,
+        load: JsonLoad,
         network: JsonNetwork,
         storage: JsonStorage,
         processes: JsonProcesses,
@@ -2505,6 +2506,12 @@ pub fn render_json(app: &App) -> io::Result<()> {
         uptime_secs: u64,
     }
     #[derive(Serialize)]
+    struct JsonLoad {
+        load_avg_1m: Option<f64>,
+        load_avg_5m: Option<f64>,
+        load_avg_15m: Option<f64>,
+    }
+    #[derive(Serialize)]
     struct JsonCpu {
         vendor: String,
         model: String,
@@ -2642,6 +2649,11 @@ pub fn render_json(app: &App) -> io::Result<()> {
             pp1_watts: app.pp1_power_w,
             dram_watts: app.dram_power_w,
         },
+        load: JsonLoad {
+            load_avg_1m: app.load_avg.map(|(a, _, _)| a),
+            load_avg_5m: app.load_avg.map(|(_, b, _)| b),
+            load_avg_15m: app.load_avg.map(|(_, _, c)| c),
+        },
         network: JsonNetwork {
             interfaces: app
                 .net