docs(seam): cite hub seam-index + PDR-0045; dissolve self-appointed steward role

[tachyon-beep]

Executes weft hub decision PDR-0045 (hub reclaims the seam-index canon; closes weft-dbaada5883 condition 2). Hub tracking: weft-83c25d96e3.

What

tests/conformance/seam_registry.json is now declared a producer-contributed conformance MIRROR — the canonical seam-index is hub-owned at weft/contracts/seam-index.json. This PR removes wardline's self-appointed cross-seam-arbiter role and the cross-sibling dispatch, replacing them with hub-PDR citations:

• legis→warpline preflight row: the two rulings now CITE hub PDRs — reverify-drop → PDR-0037, legis-conforms-down → PDR-0045 — instead of asserting a wardline "steward decision." The former "false freeze" verdict is updated to RESOLVED (legis 1.4.0 rewired to WarplineMcpClient; HttpWarplineClient gone from src), with the residual legis consumer-oracle re-freeze tracked as a distributed legis-CI task (weft-51699a641c). The attestation-row "OBLIGATION" dispatch is reframed as a described warpline-side gap.
• test_seam_registry.py: docstring canon-provenance note (mirror, not canon).
• program plan: SUPERSEDED banner — the P0-W2/P8-W2 "populate hub FROM registry + sync-lint" direction is reversed (the mirror CITES the hub index; drift-check is a wardline-side source-drift job, never a hub-side lint).

Safety (docs/prose only, gate-neutral)

The conformance gate asserts structure only and never parses "steward"/"ruling". Verified (incl. an independent adversarial pass):

• git grep -i steward → 0 matches (the completeness bar)
• all structural fields byte-identical to base; bar_verdict stays gap; evidence_paths untouched; authority/consumer unchanged
• pytest tests/conformance/test_seam_registry.py → 6 passed; pytest tests/conformance/ → 304 passed, 1 pre-existing env skip
• JSON valid (40 rows)

Release mode: additive/docs-only → ships solo, no v* tag (the gate is test-only, not in the wheel).