burn-down(docs): relocate upgrade-shutdown-contract to bdchatham-designs (Design 05)

[bdchatham]

Phase-B pilot of the design-artifact relocation (Design 05 / PLT-497) — the burn-down half. Design artifacts live with their DRI, not in code packages; these two docs relocate to bdchatham-designs.

• docs/upgrade-shutdown-contract/DESIGN.md + ISSUE.md → bdchatham-designs designs/upgrade-shutdown-contract/ (paired PR feat: enable gRPC on validator mode (parity with sei-infra canonical) #19, classified + provenance-stamped).

Note: docs/ is not fully evacuated by this PR — docs/config-manager/DESIGN.md remains (it's also a /lingua corpus exemplar, so its move carries a corpus-cite update) and is handled in the Phase-C fan-out. sei-config's end-state completes then. (The squash-merge message will reflect this; the original branch commit's "fully evacuates" wording is superseded.)

Inbound-reference audit (gating, Design 05 §3.1):

git grep -nI -e 'upgrade-shutdown-contract' -e 'docs/upgrade-shutdown' -- ':!docs/'
→ 0 hits

No .go/runtime references, no doc-links — clean removal, no stub.

Rename map (for lineage re-pointing by the TPM backfill):

was (sei-config)	now (bdchatham-designs)
docs/upgrade-shutdown-contract/DESIGN.md	designs/upgrade-shutdown-contract/DESIGN.md
docs/upgrade-shutdown-contract/ISSUE.md	designs/upgrade-shutdown-contract/ISSUE.md

⚠️ Merge order: merge the add-PR (bdchatham-designs#19) first, then this. · Linear: PLT-497

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Documentation-only deletions with no code or in-repo link updates; risk is mainly merge ordering if the destination PR is not merged first.

Overview
Burn-down relocation (Design 05 / PLT-497): removes the upgrade-shutdown-contract design pair from sei-config now that the content lives in bdchatham-designs (designs/upgrade-shutdown-contract/, paired add PR).

This PR only deletes docs/upgrade-shutdown-contract/DESIGN.md and docs/upgrade-shutdown-contract/ISSUE.md. There is no stub, no runtime or .go reference updates in-repo—the inbound-reference audit reported zero hits outside docs/. Other material under docs/ (e.g. config-manager) is unchanged here and moves in a later phase.

Merge order: land the bdchatham-designs add PR first, then this removal.

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