F152: document existing harness quality gate path

[fall-out-bug]

Summary\n- captured the 2026-04-29 Fireflies critique as F152 commercial-discovery evidence\n- added an existing-harness quality gate adoption reference\n- updated Quickstart, product surface, project map, roadmap, and workstream index routing\n\n## Verification\n- go run ./cmd/sdp-doc-sync --mode check\n- go run ./cmd/sdp-protocol-check --format json\n- git diff --check\n\nNote: strict doc sync still reports inherited backlog/link issues outside this change; non-strict doc sync reports 0 errors and 45 existing warnings.

[github-actions]

SDP Auto-Attestation

Field	Value
Branch	docs/F162-quality-gate-docs
Commit	2088e3e2
Changed files	7
Tests	✅ pass (5726 passed, 0 failed)
Lint	✅
Scope	✅ no linked workstreams — auto-attested from CI observation
Attestation generation	✅
Coverage	⚠️ 65.23345724907065%
Signed	✅ Sigstore bundle
Beads	none

Full attestation report

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Generated by SDP auto-attestation