fix(everything-server): normalize streamed tool responses

[lucarlig]

Normalizes streamed tools/call results from the bundled TypeScript everything-server so modern 2026-07-28 responses include the required resultType: "complete" discriminator.

Motivation and Context

The stateless JSON response helper adds the required discriminator, but the streamed tools/call branch wrote SSE frames directly and bypassed that normalization. The bundled reference fixture therefore produced schema-invalid modern-wire results for all seven streamed tool-call fixture scenarios.

This change centralizes stateless result normalization, applies it before both JSON and SSE output, and extends the existing fixture-to-fixture coverage to all seven streamed tool scenarios.

Fixes #461.

How Has This Been Tested?

• npm test -- src/scenarios/server/all-scenarios.test.ts — 55/55 tests passed, including all seven streamed tool scenarios on the 2026-07-28 wire
• npm test — 44 test files, 531/531 tests passed
• npm run check
• npm run build
• node dist/index.js server --url http://127.0.0.1:43117/mcp --spec-version 2026-07-28 --scenario tools-call-simple-text --verbose — 2/2 checks passed

Breaking Changes

None. This corrects the bundled reference fixture's output to match the 2026-07-28 wire schema. It does not change public CLI, configuration, scenario, or check-ID interfaces.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

This is a focused reference-fixture correction and regression test. It does not add or change a conformance scenario, requirement, or check ID, so scenario registration, traceability updates, and external SDK validation are not applicable. No new error paths or documentation requirements are introduced.

[lucarlig]

@pcarleton @felixweinberger, could one of you approve the first-time-contributor Actions runs and review this focused everything-server fix? It resolves #461 and has full local validation: 531/531 tests, build, check, and all seven streamed tool scenarios on the 2026-07-28 wire.