QBI v2 content: live SSTB crosswalk + evidence-anchored priors

[MaxGhenis]

Summary

Fills #534's fail-closed v2 engine with real, evidence-anchored content. v1 remains the production default; flipping it is a separate, deliberate change gated on the v3 evidence and the ledger anchors (ledger#120/#121).

• sstb_crosswalk_v1.json (status: live) — 101 census 2018-occupation entries (the wired spine) + 27 census 2017-industry entries (future seam), each with reg-cited rationale. Probability tiers per the supervisor adjudication: clear SSTB = 1.0 (53 occupation codes: physicians through athletes); unlisted/explicit-non-SSTB = 0 (documented neighbor lists carried in the resource); ambiguous = 0.30 default, 0.20 health technician/assistant tier, 0.25 hospital/facility industries, 0.10 lean-non-SSTB — every prior provisional: true with the §1.199A-5(c)(1) de-minimis basis string. Reputation-or-skill deliberately unmapped (income-type test). Verified stable across the 2022 census code vintage.
• Passive pass-through SSTB priors by threshold band, derivation shown in the resource: OTA WP-118's SSTB restriction removes $58.24B of $221.00B of unconstrained deductions → 0.264 below-threshold; the income-exception step implies 0.170 above.
• REIT/PTP re-anchoring: receiving-probability × Beta scales set against SOI Pub 4801 (line 6 $21.07B REIT/PTP income); the full-artifact replay lands at $20.943B = 0.994× the anchor (diagnostic test with a provisional [0.3×, 3×] band). BDC keeps v1 scale, documented as unanchored.
• Qualification derivation content: self-employment and farm operations become law-derived; partnership/S-corp, farm rent, rental, and estate keep documented priors with rationale strings naming exactly what each proxies and its v3 replacement path.

Verification (supervisor, independent)

Full workspace suite with restricted artifacts: 3,260 passed, 0 failed; ruff clean; resource declared; probability tiers independently re-derived from the shipped JSON and matched to the adjudication spec exactly.

Stacked on #535 (→ #534 → #532); the PR gate fires per layer as the stack merges toward main.

Refs #530

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