Importing a shareable profile that contains tagger scripts leaves the scripts disabled, so none of them run.

Steps to reproduce

1. Import a profile whose .toml file has a [[scripts.tagging]] section.
2. Enable the imported profile.
3. The tagger scripts do not run.

Cause

The per-profile "Enable tagger scripts" master toggle gates all tagger script processing. On import the scripts were added to the profile but this toggle was never set, so it stayed off. It was also not written on export, so a backup could not restore its state.

Fix

Handle the master toggle together with the scripts, depending on export mode:

Import: if the file has an explicit enable_tagger_scripts value under [scripts] (backup export), honor it. Otherwise (share export) enable the toggle when at least one new script was imported.

Export: backup mode writes the exact toggle value so a restore is faithful. Share mode omits it; the importer re-enables scripts because the [[scripts.tagging]] section is present.

Why the modes differ: a backup is a faithful snapshot of your own config, so the on/off state must be preserved.
A shared profile is meant to run its scripts on the recipient's machine, so the toggle is implied by the presence of scripts.
Writing it in share mode would be harmful: because a profile setting is an override, an author's "off" value would force the recipient's tagger scripting off, silently disabling their scripts too.

Initially reported in https://community.metabrainz.org/t/picard-3-release-candidate-2/815620/27?u=zas