Improve Lightning Network Feedback for New Users

[Romeux]

The current feedback provided by Electrum when attempting to use the Lightning Network without an active channel can be confusing, especially for new users. When users try to generate a Lightning invoice in the "Receive" tab without having an active Lightning channel, they see the message:

"You must be online to receive Lightning payments."

This message is misleading because:

The "online" status indicator (green dot in the bottom right) already confirms that the user is online.
The actual issue is not the online status but the lack of an active Lightning channel with sufficient inbound liquidity.
This creates unnecessary confusion, especially for users unfamiliar with the technical requirements of the Lightning Network. It also gives the impression that the wallet might be malfunctioning.

Steps to Reproduce
Open a Lightning-enabled Electrum wallet.
Go to the "Receive" tab and attempt to create a Lightning invoice without having an active Lightning channel.
Observe the misleading error message: "You must be online to receive Lightning payments."
Proposed Solution
Update the error message to clearly communicate the real issue and guide the user on how to resolve it. For example:

Replace the current message with:
"You must have an active Lightning channel to receive payments. Open a Lightning channel or request inbound liquidity from a third party to enable receiving."

This message:

Clearly states the requirement for an active channel.
Provides actionable advice on what the user should do next.
Additionally:

Consider adding a brief tooltip or help button in the "Receive" tab to explain the basics of Lightning channels and their requirements for receiving payments.
Optionally, include a direct link to the "Channels" tab or an external guide on how to set up and manage channels.
Benefits
Improves clarity for new users who may not understand the technicalities of the Lightning Network.
Reduces frustration and support requests caused by the current misleading message.
Makes Electrum more user-friendly and accessible for non-technical users while maintaining functionality for advanced users.
Environment
Electrum version: (provide your version, e.g., 4.4.5)
Operating system: (e.g., Windows 11, macOS Ventura, Ubuntu 22.04)
Lightning enabled: Yes
Steps attempted: Receiving Lightning payments without an active channel.

[ecdsa]

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