#244 fix(runtime): surface writeback no-receipt failures

Summary

• wrap runtime writeJsonFile so missing Relayfile writeback receipts become first-class WritebackErrors with state: no_receipt
• expose normalized writeback status helpers and WritebackError from runtime/client barrels
• add runtime coverage for receipt success and no-receipt failure compatibility with WorkforceIntegrationError

Dependency

• Pairs with AgentWorkforce/relayfile-adapters#215. This PR is written to compile with the current adapter-core package and will automatically use adapter-core's normalizer/error exports when that package release lands.

Verification

• pnpm install --frozen-lockfile
• pnpm --filter @agentworkforce/persona-kit build
• pnpm --filter @agentworkforce/runtime test (94/94 pass)

Part of AgentWorkforce/cloud#2291 W6 follow-up.