Add provider-local environment overlays

[christso]

Summary

• Add providers[].environment support for inline recipes and file:// refs in eval/provider catalog/config provider declarations.
• Compose candidate provider overlays with suite/test/case environments, preserve layered provenance, and emit explicit conflicts for unsafe setup/cwd/Docker overlaps.
• Prepare grader provider-local environments separately for grader invocation, without applying them to candidate execution.
• Include provider-local environment refs in task/eval bundle serialization and docs for the next contract.

Validation

• bun test packages/core/test/evaluation/environment-host-runtime.test.ts packages/core/test/evaluation/loaders/environment-recipe.test.ts packages/core/test/evaluation/loaders/config-loader.test.ts
• bun test apps/cli/test/commands/eval/task-bundle.test.ts
• bun run lint
• bun run typecheck
• bun run build
• Live dogfood via local OpenAI-compatible proxy at http://127.0.0.1:10531/v1:
  • candidate provider: CLI wrapper that calls the proxy and reads a provider-local environment marker from cwd
  • grader provider: live OpenAI-compatible provider selected with --grader-provider live-grader
  • result: 1/1 passed at 100%

Evidence

• Private evidence branch: agentv-private:evidence/av-f7w4-provider-env-overlays
• Evidence commit: b838ec7
• Evidence includes the source eval/providers/environment recipes, run bundle, artifact tree, and provenance sidecar showing distinct base/provider composition layers.

Bead: av-f7w4

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