feat(integrations): add catalog discovery CLI commands (search, info, catalog list/add/remove)

[mnriem]

IntegrationCatalog and the catalog JSON files (integrations/catalog.json, integrations/catalog.community.json) already exist, but the CLI has no commands to interact with them. Users can only browse integrations via specify integration list.

Missing CLI commands

Missing from specify integration	Present in specify extension / specify preset / specify workflow
search	Search catalogs with --tag / --author filters
info <id>	Show detailed information about an integration
catalog list	List configured catalog sources
catalog add <url>	Add a catalog source
catalog remove <index>	Remove a catalog source by index

Not applicable to integrations

• add / remove — integrations intentionally use install / uninstall / switch since they configure which agent you're using, not additive stacking
• enable / disable / set-priority — same reason; integrations aren't stacked

Reference

• Catalog class: src/specify_cli/integrations/catalog.py (IntegrationCatalog)
• Catalog files: integrations/catalog.json, integrations/catalog.community.json
• Extension catalog CLI (reference pattern): src/specify_cli/__init__.py (extension catalog, extension search, extension info)