docs(discovery): rename Catalog Entry mediaType field to type (ADR 0014)

[tadasant]

What

Adapts the MCP Catalog Entry in docs/discovery.md to AI Catalog PR #37 / ADR 0014, which renames the CatalogEntry.mediaType member to type and reframes its description as an open-text type identifier rather than a strict IANA media type.

Changes (docs-only, docs/discovery.md):

• Renames the mediaType member to type in the Catalog Entry table.
• Updates the member description to mirror ADR 0014: "An identifier specifying the type of the referenced artifact."
• Updates the type key in all four example catalog entries.
• Updates the client-validation prose (type set to … / "ignore entries with unrecognized types").

Scope decision — value deliberately kept as application/mcp-server-card+json

This PR renames the field only. The value stays application/mcp-server-card+json and is not changed to ADR 0014's known-type application/mcp-server+json. Rationale:

• ADR 0014 explicitly makes type an open-text format ("any string value is accepted"); application/mcp-server+json is a non-binding "known type," and ecosystem types are "governed externally" (i.e., by MCP). So keeping a more precise MCP-governed value is compatible with ADR 0014, not a contradiction.
• This repo deliberately chose application/mcp-server-card+json over application/mcp-server+json (issue MCP Catalog mediaType (application/mcp-server+json) diverges from AI Catalog's application/mcp-server-card+json #9 / PR docs: align Catalog mediaType with AI Catalog spec #18) to avoid colliding with the MCP Registry's server.json concept — a distinction the README documents in "Relationship to the MCP Registry."

Flag for maintainers: AI Catalog's ADR 0014 known-types list uses application/mcp-server+json for MCP. Whether this repo should also adopt that value (reversing issue #9 / PR #18 and re-introducing the server.json naming collision) is a separate, more consequential decision and is intentionally out of scope here. Happy to file a cross-repo issue if maintainers want to pursue it.

What is intentionally NOT changed

• The Server Card document's own HTTP media type (Accept / Content-Type negotiation, the reserved /server-card location prose). That is a genuine IANA media type, not the renamed catalog field, and ADR 0014 does not touch it.
• schema.ts / schema.json — the Server Card schema has no mediaType/type member; this convention lives only in the discovery doc.

This is a separate PR from #31 (the urn:air: identifier adaptation); both touch docs/discovery.md and may need a trivial rebase depending on merge order.

Verification

• npm run check — schema.json up to date, tsc --noEmit clean
• npm run validate — all 7 examples pass
• npm run format:check (prettier over tracked *.ts/*.json/*.md) — clean, including markdown table re-alignment
• Verified zero mediaType field tokens remain (git grep mediaType → no matches)
• Verified the Server Card HTTP media-type prose was left intact (no over-reach)
• Independent fresh-eyes subagent review: APPROVE (rename complete & correct; scope decision defensible; CI green)
• Cross-checked against ADR 0014 raw text (PR #37, branch jbu/adr-0014-mediatype-to-type)

🤖 Generated with Claude Code

[tadasant]

Let's hold on merging until the AI Catalog PR lands