[muhammad-abdallah]

Summary

This PR improves the ExpressLRS Backpack documentation by adding a centralized section explaining how to access Backpack web interfaces using local network hostnames.

The new section includes:

• A table documenting the TX, AAT, VRX, and Timer Backpack .local addresses.
• An explanation of mDNS and local network requirements.
• Troubleshooting advice when hostname resolution fails.
• Instructions for accessing the web interface using 10.0.0.1 in access-point mode.
• Links to the existing TX and VRX Backpack setup guides.

Motivation

The TX and VRX hostnames were already mentioned in their respective setup guides, but the information was scattered, and the AAT and Timer addresses were not documented in the main Backpack documentation.

This change makes the information easier for users to find.

Validation

• Verified that all four hostnames are present.
• Verified that both linked setup documents exist.
• Ran git diff --check successfully.
• No firmware or application code was modified.

Documentation build and hardware behavior have not been tested locally.

Related issue

Addresses #528.