Docs: troubleshooting guide for missing Actuators tab (logging-based diagnosis)

[DonLakeFlyer]

"My Actuators tab doesn't show up" is a common support complaint (most recently in #14789). QGC already logs exactly why the tab was hidden, but users don't know how to capture that information. We need a docs page explaining how to self-diagnose.

Background

The Actuators tab only appears when actuator metadata is successfully retrieved via the MAVLink Component Information protocol (COMP_METADATA_TYPE_ACTUATORS). The metadata is downloaded from the vehicle via MAVLink FTP, with an HTTP fallback URL advertised by the firmware. If both fail (or the metadata's show-ui-if condition is false), QGC silently falls back to the legacy Motors page.

QGC logs the reason under these logging categories:

• Vehicle.Actuators.PX4AutoPilotPlugin — logs "Actuators page will NOT show because: ..." with the specific reason (no metadata / init failed / show-ui-if false)
• ComponentInformation.RequestMetaDataTypeStateMachine — logs metadata download failures including the failing URLs
• Vehicle.FTPManager — shows the vehicle-side metadata download traffic

Docs to write

Add a troubleshooting page (or section under the PX4 Actuators setup docs) covering:

1. What drives the Actuators tab appearing (component metadata, not firmware version alone)
2. How to enable the relevant logging categories in Application Settings → App Log Viewer → Categories
3. How to capture: enable categories → connect vehicle → open Vehicle Setup → save App Log
4. How to read the common failure signatures (metadata 404 on the fallback URL, FTP download failure, show-ui-if false)
5. What to include when filing a support request/issue