fix(schema): reject authored eval YAML workers - #1578

Summary

Eval files can no longer author concurrency through workers; concurrency is now explicitly an operator/run setting from --workers, project config defaults, or target/provider caps. This keeps eval YAML focused on task definition, target binding, and policy while preserving the existing runtime worker execution path.

The parser, validator, schema, SDK YAML authoring helpers, TS eval materialization, and eval bundle generation now reject or stop emitting authored workers. Examples and docs now point users toward CLI/config concurrency instead of embedding worker counts in eval files.

Validation

• bun install
• bun --filter @agentv/core build && bun --filter @agentv/sdk build
• bun --filter agentv build
• bun test packages/core/test/evaluation/experiment.test.ts packages/core/test/evaluation/eval-inline-experiment.test.ts packages/core/test/evaluation/loaders/config-loader.test.ts packages/core/test/evaluation/loaders/ts-eval-loader.test.ts packages/core/test/evaluation/validation/eval-validator.test.ts
• bun test packages/core/test/evaluation/validation/eval-file-schema.test.ts
• bun test packages/sdk/test/eval-authoring.test.ts
• bun test apps/cli/test/eval.integration.test.ts apps/cli/test/commands/eval/vscode-worker-limit.test.ts apps/cli/test/commands/eval/bundle.test.ts
• bun run validate:examples
• Targeted bunx biome check on modified TypeScript files

Not run: full bun run verify; live provider dogfood.