A `catalog=<name>` deep link now resolves the name against the live plugin
catalog feed (the same `/docs/api/plugins.json` the Capabilities → Plugins
picker renders) and opens the Install Plugin dialog in its reviewed/pinned
catalog mode — identical to an in-app catalog pick, via one shared
`openCatalogPluginInstall` helper the Plugins tab now uses too.
The `catalog` param claims the link outright: an unknown, invalid, or
unresolvable name is a clear error toast and nothing else. It is never
reinterpreted as a git identifier, so a link cannot smuggle an unreviewed
repo behind a familiar-looking name (a `repo=` riding along is ignored).
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