refactor(plugins): one install prompt for drivers and export formats

[datlechin]

Why

Four copies of the same confirm, download and error flow: two SwiftUI modifiers (connection and type) and two AppKit prompts (driver for a file, export format). Two alert messages also pointed at a plugin marketplace the app no longer has.

Change

• PluginInstallPrompt replaces MissingDriverPluginPrompt and MissingExportFormatPrompt: one confirm, run and error path, on PluginInstallProgressPresenter.run.
• One generic pluginInstallPrompt(for:type:onInstalled:) modifier replaces the connection and type modifiers. A failed install now reports through AlertHelper, like the other two prompts.
• The presenter's begin, update and end are private; history comments and file headers go.
• "plugin marketplace" is gone from the not-installed messages; catalog synced from Xcode's stringsdata.

Verified

Build passes; no new test, the change is alert and panel presentation with no new logic.