Hide settings rows whose key the aircraft cannot read

The Mavic Pro remote reports GIMBAL_CONTROL_SPEED_COEFFICIENT as supported but
fails every read, so "Gimbal dial speed" sat on "—" forever. The key bridge
now reports a failed seeding read, and the row hides like an unsupported one
until a value does arrive.

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

Fly App/android/app/src/main/kotlin/com/pilotvault/flyapp/KeyBridge.kt

@@ -113,7 +113,11 @@ class KeyBridge(private val ctx: BridgeCtx) : SubBridge {
                         ctx.emit(mapOf("type" to "key", "id" to id, "value" to KeyValues.toDart(value)))
                     }
 
-                    override fun onFailure(error: DJIError) = Unit
+                    // Supported but unreadable (the Mavic Pro remote's gimbal dial
+                    // speed): say so, or the row waits on "—" forever.
+                    override fun onFailure(error: DJIError) {
+                        ctx.emit(mapOf("type" to "key", "id" to id, "unreadable" to true))
+                    }
                 })
                 result.success(id)
             }