[PR-018] Make standalone Corpus tests self-contained

[ilyar]

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Make standalone Corpus tests self-contained

Outcome

The Corpus package test command succeeds from a clean checkout without relying
on the root workspace pretest or a manually built receipt package.

Scope

• Product: product/proof-runner
• Allowed paths: packages/corpus/package.json, workspace build/test
  dependency ordering, and focused bootstrap regression coverage

Acceptance

• After pnpm install --frozen-lockfile,
  pnpm --filter @ever-guild/proof-runner-corpus test passes without a
  manual build step.
• Corpus pretest builds every workspace package required by its integration
  imports, including @ever-guild/proof-runner-metadata and
  @ever-guild/proof-runner-receipt.
• A regression guard fails if the standalone test again depends on
  artifacts produced only by the root pretest.
• Root pnpm test, Corpus lint/typecheck/test, and manifest checksum
  verification pass.
• Required CI and independent review pass on the implementation commit.

Evidence

• Reproduced on product main
0ac73a10c864a55e24f0b64595567bb18a10298c after a clean frozen install.
• Corpus lint and typecheck pass; the clean standalone test loads 30 tests,
  then its integration suite fails first because Vite cannot resolve
  @ever-guild/proof-runner-metadata from apps/api/src/server.ts.
• If metadata was built earlier by pnpm run test:deployment, the same
  standalone Corpus test advances to the next missing artifact and cannot
  resolve @ever-guild/proof-runner-receipt from
  apps/api/src/evidence-bundle.ts.
• Root pnpm test remains green because the root pretest builds the receipt
  package first.
• Product tracking:
  Issue #43.