Batch the Fly App's telemetry and split it per subsystem

The GO 4-style HUD needs far more live data than the bridge sent, and
pushing every SDK callback straight to Dart would rebuild the screen
dozens of times a second. This is the telemetry foundation (plan P1).

On the Kotlin side, every source now writes into a TelemetryHub that
emits one telemetry event per tick: flight-controller state, gimbal and
vision at up to 10 Hz, battery, links, RC, storage and camera settings
folded in at up to 2 Hz. Each event carries the full latest snapshot, so
a consumer that drops packets never loses a slow group. New bridges
cover batteries (every pack, cell voltages, warning thresholds), link
quality and RC battery, diagnostics, and obstacle sensing per sensor.
KeyBridge adds generic getKey/setKey/listenKey over KeyManager for the
settings rows to come. The flight controller also gains smart-RTH
confirmation and simulator start/stop.

On the Dart side, FlightModel now owns one ChangeNotifier per subsystem
(aircraft, battery, links, camera, gimbal, vision, alerts, mission), so
a HUD widget can listen to just the one it draws. TelemetryReducer
routes events into them, only notifies groups that changed, and gives
FlightModel one notification per tick. Flat getters keep the existing
screens working. Diagnostics become graded, de-duplicated alerts.
Settings > About > Telemetry inspector shows every field live and can
start the simulator.

Battery no longer arrives as its own event, so the API Server reads the
percentage from the telemetry snapshot (the old event is still accepted).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

API Server/internal/hub/models.go

@@ -149,4 +149,12 @@ func applyTelemetry(t *Telemetry, raw map[string]any) {
 	if v, ok := toFloat(raw["velocityZ"]); ok {
 		t.VelocityZ = &v
 	}
+	// Since the Fly App batches telemetry, the battery rides along as a nested
+	// group whose top-level percent is the weakest pack. The standalone
+	// "battery" event is still accepted for older app builds.
+	if b, ok := raw["battery"].(map[string]any); ok {
+		if p, ok := toInt(b["percent"]); ok {
+			t.BatteryPercent = &p
+		}
+	}
 }