feat(channels): Surface C — related-channels band on /topics/* (P3)

[jung-thomas]

Surface C — Related channels band on /topics/* (Phase 3)

External-channels integration, Phase 3. Adds a curator-reviewed crosswalk from channels to site topic tags and renders a "Related channels" band on topic term pages.

Spec: docs/superpowers/specs/2026-09-04-external-channels-integration-design.md (§5.3, §9, §13, §14, §15, §16)
Plan: docs/superpowers/plans/2026-09-04-external-channels-p3-topic-bands.md

What's included

• Model — ChannelTopicMap crosswalk entity (channel, topicTag in mdFormat, relevance, authoringStatus), unique (channel, topicTag), @cds.persistence.journal + regenerated migration table.
• Admin — AdminService.ChannelTopicMap draft-enabled projection + Fiori Elements admin app (prefix ctm) with shell registration, for curators to review/correct and promote AI_SEEDED → REVIEWED.
• Seed — idempotent LLM draft pass (npm run seed-channel-topic-map): upserts on (channel_ID, topicTag), preserves REVIEWED rows, writes AI_SEEDED. AI SDK + chat-settings resolver lazy-imported off the srv-qa boot path.
• Payload — buildTopicDetailPayload joins the crosswalk: REVIEWED-gated, published-channel + non-broken-link filtered, ordered by relevance desc, capped at 5, empty-safe.
• Render — empty-safe <section class="topic-channels"> band with owner badges + external links (rel="noopener"); ships via the existing topic-<slug> publish pipeline (CAP-SSR BLOB, not Hugo).
• e2e — tolerant post-deploy nudge; self-skips without SMOKE_BASE_URL.

Verification

• Per-task review (spec + code quality) APPROVED on all 7 tasks; whole-branch review CLEAN; end-to-end data contract confirmed (seed mdFormat write == payload join key == render shape).
• CDS gates: check-cds-build-staging 0, check-srv-qa-cp-list 0.
• Unit suite green — all P3 tests pass. (Pre-existing hugo-apps/selfie failures are missing optional deps in this worktree, unrelated to P3.)

Scope boundary

ChannelSubmissions (P4) is explicitly out of scope.

🤖 Generated with Claude Code