fix(ui): validate MCP server transport url and support oci packages

[lleon-at-navteca]

Description

Motivation:

The Add Server UI allowed creating invalid payloads for MCP servers using streamable-http or sse transports, which caused backend validation errors on publish. It also defaulted package registryType to npm, which does not match the containerized MCP server flow.

Resolves #405

What changed:

• Added package transport URL support in the Add Server dialog.
• Added client-side validation:
  • package transport URL is required for streamable-http and sse.
  • remote URL is required for streamable-http and sse.
• Changed default package registryType from npm to oci.
• Added oci option to the package registry type selector.
• Switched $schema default to the canonical schema URL.
• Replaced free-text remote type input with a constrained selector (stdio, sse, streamable-http).
• Added UI tests for:
  • oci default behavior.
  • submit blocked when package streamable-http URL is missing.
  • payload includes transport.url for streamable-http.
  • submit blocked when remote sse URL is missing.

Change Type

/kind fix

Changelog

fix(ui): validate transport URLs for streamable-http/sse and default MCP package registry type to oci in Add Server dialog

Additional Notes

• The backend already enforces transport URL requirements; this PR aligns frontend behavior with existing server validation.
• Tests added in ui/components/tests/add-server-dialog.test.tsx.
• Local test run passed for the new test file.