feat(harness): engine-agnostic PII redaction at the user-message layer #47

Job	Run time
build (agentos-server, packages/agentos-server/Dockerfile)	1m 48s
build (harness-server, examples/Dockerfile.harness, examples/harness-server.ts, harness)	5m 7s
build (computeragent-server, examples/Dockerfile.harness, examples/computeragent-server.ts, harness)	5m 26s
build (agentos-spa, agentos/Dockerfile, spa)	30s
	12m 51s

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