feat: implement MCP server search functionality and registry integration

[vvnsrzn]

MCP Search

Adds an MCP Registry search tab to the "Add Server" modal, allowing users to discover and add servers from the official registry in one click.

When selecting a server, the name, URL, and required authentication headers are automatically pre-filled with description hints — and mandatory headers cannot be removed.

Existing custom servers can now be edited directly from the server list

A new /api/mcp/registry endpoint proxies the MCP registry with a 5-minute cache.

[chatgpt-codex-connector]

💡 Codex Review

chat-ui/src/lib/components/mcp/AddServerForm.svelte

Lines 104 to 105 in e121362

	// Filter out empty headers
	const filteredHeaders = headers.filter((h) => h.key.trim() && h.value.trim());

Enforce required headers before dropping empty rows

Required registry headers can still be removed by clearing both inputs: validate() ignores rows where key/value are both empty, and this filter then drops those rows entirely on submit. In practice, a user can bypass the “non-removable” UI for mandatory auth headers and save a broken server config that fails health checks/connection.

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[chatgpt-codex-connector]

Represent required headers explicitly, not via description

The form treats description as the required/locked signal (!header.description controls whether a header is removable), but registry header descriptions are optional. That means a header marked required by the registry but lacking a description is shown as removable/optional, so the UI can silently violate required-auth metadata.

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