v1.5.1 — extract selected files from the Archives search results

GUI fix: the Archives search panel now has its own 'Extract selected…' button. Previously the bottom Extract button always acted on the browse file tree, so selecting a file in search and extracting could silently pull the wrong file (e.g. asking for ./etc/hosts and getting ./etc/brltty). Selecting a version row extracts that exact copy; a path row extracts its newest version.