Local directory links became broken text previews and local paths kept a
useless Download (#101683). Main-process normalization now answers with
typed non-previewable results ('directory'/'missing') instead of
overloading directories as index.html and dropping missing paths to null,
and the delivered-file card classifies its target to offer the native
folder action for directories, reveal-in-file-manager for existing local
files, and a not-found report for dead links. Remote-backend targets keep
the gateway-backed Download/preview actions.
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