feat(mcp): MCP Registry metadata — mcpName + server.json

[jiashuoz]

Summary

Prep for publishing @e2a/mcp-server to the official MCP Registry. Two artifacts:

1. mcp/package.json — adds mcpName: "io.github.mnexa-ai/mcp-server". This is the verification handshake the Registry uses at publish time: it confirms the npm package belongs to the publisher claiming the registry name. The convention io.github.OWNER/NAME is required for GitHub-based auth (lowercased per the Registry's namespacing rules). Also bumps version 0.3.0 → 0.3.1 — two fixes merged since the 0.3.0 tag warrant a publish (single-agent prefetch feat(mcp): single-agent default at session init #98 + hosted-MCP example variants docs(examples): add hosted-MCP variant to ADK, LangChain, OpenAI Agents #99).

2. mcp/server.json — the Registry's canonical server descriptor. Lists both transports in one entry:

   • packages[] → stdio via @e2a/mcp-server@0.3.1 with three env vars (E2A_API_KEY required+secret, optional E2A_AGENT_EMAIL, optional E2A_BASE_URL)
   • remotes[] → streamable-http at https://mcp.e2a.dev/mcp with Authorization: Bearer {e2a_api_key} header (the registry exposes e2a_api_key as a user-configurable variable)

Validated against schema 2025-12-11 — passes structural checks, description fits the 100-char limit.

Publish flow (post-merge, manual step required)

This PR doesn't publish — it lands the metadata. To actually push to the Registry:

# 1. After merge, tag the release. publish-mcp.yml fires and ships
#    @e2a/mcp-server@0.3.1 to npm with the mcpName field baked in.
git tag mcp-v0.3.1 && git push origin mcp-v0.3.1

# 2. Install the Registry's publisher CLI.
brew install mcp-publisher

# 3. Auth interactively with GitHub OAuth.
mcp-publisher login github

# 4. Publish. Reads ./server.json, verifies that
#    @e2a/mcp-server@0.3.1 on npm has the matching mcpName field,
#    then writes the listing.
cd mcp && mcp-publisher publish

Why this matters

The Registry is the upstream that several downstream catalogs (mcp.directory, Glama, Smithery, mcpmarket) cross-reference. Listing here propagates the npm + hosted info to those catalogs on their next sync, often without separate submissions.

Test plan

• mcp/server.json validates against schema 2025-12-11 (manual jsonschema check)
• mcp/package.json still parses; version bump consistent with the npm pipeline
• After merge + tag + publish: confirm Registry shows e2a at https://registry.modelcontextprotocol.io/v0/servers/io.github.mnexa-ai/mcp-server

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