burn-down(docs): relocate 13 design artifacts to bdchatham-designs (Design 05 Phase-C)

[bdchatham]

Phase-C fan-out, sei-k8s-controller batch (Design 05 / PLT-497) — the burn-down half (paired add: bdchatham-designs#21).

Removes 13 design artifacts now relocated to the designs repo, and repoints controller-app-config's 3 inbound doc-links (README.md, CLAUDE.md, config/manager/manager.yaml comment) to the new location.

Stays in docs/ (not evacuated this round):

• Sonar-gated (real consumers cite by path/anchor — Design 05 §5): design/seinode-task-lld.md (Go + generated CRD YAML), design/test-harness-lld.md (Go + CI), seinode-task.md (headings are cited anchors for the PLT-489 gov-ops skill)
• Cross-DRI: design-e2e-kind-harness.md (Amir → amir-deris-designs, separate PR)

Audit (canonical origin/main 73701f1): controller-app-config had 3 doc-links (repointed); the other 12 relocated docs had 0 inbound refs. Prepared in an isolated worktree — active feature branches untouched.

⚠️ Merge order: merge bdchatham-designs#21 first, then this. · Linear: PLT-497

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Documentation-only relocation with no controller or CRD behavior changes; merge bdchatham-designs#21 first so the new URLs exist.

Overview
Design 05 Phase-C doc burn-down: thirteen long-form design/RFC/LLD files are removed from this repo (networking/monitoring, progressive rollout, RPC migration, import volume, validator signing key, snapshot publish, composable genesis, stale targetHeight bug write-up, and the in-repo controller-app-config page).

Inbound links for app-config are repointed to the canonical schema in bdchatham-designs in CLAUDE.md, README.md, and the config/manager/manager.yaml comment (replacing docs/controller-app-config.md).

Operational docs that stay here (docs/seinode-task.md, selected LLDs, etc.) are unchanged per the PR scope.

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