chore: migrate to MCP TypeScript SDK v2

[mattzcarey]

Summary

Migrate from @modelcontextprotocol/sdk v1 to the v2 packages, pinned to the
2.0.0-beta.1 release candidate. Rebuilt on top of current main (which
refactored the tool code into src/tools/*).

• Drop @modelcontextprotocol/sdk; add @modelcontextprotocol/server@2.0.0-beta.1
  (dep) and @modelcontextprotocol/client@2.0.0-beta.1 (devDep, tests only).
• Repoint imports to the @modelcontextprotocol/server root export
  (WebStandardStreamableHTTPServerTransport, McpServer, Tool/CallToolResult
  types). The Web Standard transport still exists in v2 with the same options, so
  src/index.ts is a behavior-preserving import change.
• Low-level non-Code-Mode handlers use method strings
  (setRequestHandler('tools/list' | 'tools/call', …)); the request-schema
  exports were removed in v2.
• Wrap registerTool inputSchema/outputSchema in z.object(…) for the v2
  Standard Schema API.
• Mirror v2's wire output in the precomputed non-Code-Mode artifacts: JSON Schema
  dialect 2020-12 (was draft-07) and drop execution.taskSupport (v2 omits it
  for non-task tools). Kept byte-identical to the SDK-generated tools per
  tests/non-codemode.test.ts.
• No manual @cfworker/json-schema dependency: 2.0.0-beta.1 bundles the Workers
  validator and auto-selects it on the workerd export condition.

See MIGRATION_TRACKER.md for the full decision log.

Validation

• npm run check — format, lint, typecheck, and 261 tests pass (incl. the e2e
  suite that drives the real worker through the full Streamable HTTP transport,
  tool dispatch, and a real Worker Loader isolate call against 2.0.0-beta.1).
• npm run deploy — deployed to staging; worker boots in 107 ms with no
  bundle/boot errors.

Worker:     cloudflare-api-mcp-staging
URL:        https://staging.mcp.cloudflare.com
Version ID: a3ff901c-61ca-4e6f-bfc1-008b66b5fef8

Deployed-worker smoke checks: /.well-known/oauth-protected-resource → 200,
/.well-known/oauth-authorization-server → 200, unauthenticated POST /mcp →
401. (A full authenticated round-trip against the staging endpoint needs a
token valid on the staging Cloudflare API; that path is covered by the e2e suite.)

Notes

• 2.0.0-beta.1 is <3 days old, so installing it locally requires overriding the
  min-release-age npm setting for the intentional install.