fix(server): validate wrapped output schemas on v1

[Genmin]

Summary

• mirror input validation's fallback behavior for tool output schemas on v1.x
• validate wrapped/non-object top-level Zod output schemas directly when normalizeObjectSchema() cannot produce an object schema
• add regression coverage across the Zod v3/v4 matrix for optional, nullable, nullish, and union output schemas

Fixes #1308 for the v1.x release line.

Validation

• npm test -- test/server/mcp.test.ts -t "non-object-wrapper"
• npm test -- test/server/mcp.test.ts
• npx prettier --check src/server/mcp.ts test/server/mcp.test.ts .changeset/fix-output-schema-wrappers.md
• npx eslint src/server/mcp.ts
• git diff --check

Note: npm run typecheck -- --pretty false currently fails on unrelated existing v1.x test errors in test/integration-tests/taskLifecycle.test.ts and test/shared/protocol.test.ts (Expected 2-3 arguments, but got 1). No typecheck error points at the files changed in this PR.

[changeset-bot]

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Latest commit: 427660b

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commit: 427660b