Cascading server search - preview build

Preview build of an experimental improvement to message search, based on upstream thunderbird-android main (b4d4fdd).

What's new

• Empty search results show a message and a tappable prompt instead of a blank screen
• Server search cascades: current folder first, then the account's remaining folders, then all other accounts
• A persistent status bar with a spinner shows at all times what the search is doing (folder being searched with account name and counter, per-message download progress)
• Lasting result messages: "No messages found on the server" / "Remote search failed"

Notes

• This is an unsigned debug build for testing only - do not use it with important mail accounts
• Not an official Thunderbird release; Thunderbird is a trademark of MZLA Technologies
• Source: branch feature/cascading-server-search in this fork

Built with AI assistance (Claude).