feat: add niche + keyword_niche tables for feed diversification

[idoshamun]

Summary

Introduces the data structure (schema only) for niche-based feed diversification. Niches are the mental categories a user uses when saying "stop showing me X" — the unit at which the upcoming diversifier penalizes feed repetition.

New tables

• niche — catalog of niches, grouped into:
  • ecosystem — stack identity (js_ts, rust, python, …)
  • theme — cross-stack topics (ai_llm, sec_threats, cloud, …)
• keyword_niche — maps each keyword (tag) to:
  • primaryNicheId (NOT NULL)
  • secondaryNicheId (nullable, must differ from primary)
  • weightMultiplier — per-tag dampening (e.g. 0.3 for generic tags like programming)
  • confidence — 1=guess, 2=likely, 3=clear (for prioritizing audits)
  • labelerVersion — identifier of the labeler/taxonomy version that produced the row

How the diversifier will use it

A post's niches are derived from the niches of its tags via weighted vote (IDF × weightMultiplier, plus ecosystem boost). The MMR-style re-ranker will then penalize candidate posts whose primary or secondary niche overlaps with a higher-ranked post in the same response.

Taxonomy spec and derivation rules live in the brain doc docs/feed-niche-taxonomy.md.

Scope of this PR

• Schema only. No niche rows or keyword_niche mappings are inserted; data will be populated separately.
• No API/GraphQL changes yet — those land once we wire the diversifier.

Migration

1779878138923-PostNiches.ts creates both tables with FKs to keyword.value and niche.id, plus check constraints on bucketGroup, confidence, and the primary ≠ secondary invariant. Indexes on primaryNicheId and secondaryNicheId for join-from-niche queries (analytics + future per-niche listings).

[pulumi]

🍹 The Update (preview) for dailydotdev/api/prod (at 259e7b2) was successful.

✨ Neo Explanation

Routine deployment rolling all workloads to commit `883ffa71`, with an additive database migration that creates the `niche` and `keyword_niche` tables for feed diversification. ✅ Low Risk

This PR introduces the niche and keyword_niche tables to support feed diversification — mapping keywords/tags to niche categories (ecosystem or theme) so the feed diversifier can penalize repetitive content by niche.

The deployment follows the standard pattern: new DB and Clickhouse migration Jobs are created for the new commit hash (883ffa71), the previous migration Jobs (e0909e03) are cleaned up, and all deployments/crons are rolled to the new image tag.

🔵 Info — The PostNiches migration adds two new tables with foreign keys: keyword_niche.keyword references keyword.value (cascade delete), and both niche ID columns reference niche.id (restrict delete). These are additive-only schema changes with no modifications to existing tables, so there is no risk to existing data.

Resource Changes

    Name                                                       Type                           Operation
~   vpc-native-rotate-weekly-quests-cron                       kubernetes:batch/v1:CronJob    update
-   vpc-native-api-db-migration-e0909e03                       kubernetes:batch/v1:Job        delete
~   vpc-native-personalized-digest-cron                        kubernetes:batch/v1:CronJob    update
~   vpc-native-channel-digests-cron                            kubernetes:batch/v1:CronJob    update
~   vpc-native-sync-subscription-with-cio-cron                 kubernetes:batch/v1:CronJob    update
~   vpc-native-generate-search-invites-cron                    kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-stale-user-transactions-cron              kubernetes:batch/v1:CronJob    update
~   vpc-native-check-analytics-report-cron                     kubernetes:batch/v1:CronJob    update
~   vpc-native-temporal-deployment                             kubernetes:apps/v1:Deployment  update
~   vpc-native-validate-active-users-cron                      kubernetes:batch/v1:CronJob    update
~   vpc-native-update-source-public-threshold-cron             kubernetes:batch/v1:CronJob    update
~   vpc-native-private-deployment                              kubernetes:apps/v1:Deployment  update
~   vpc-native-user-profile-updated-sync-cron                  kubernetes:batch/v1:CronJob    update
~   vpc-native-calculate-top-readers-cron                      kubernetes:batch/v1:CronJob    update
~   vpc-native-generic-referral-reminder-cron                  kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-old-notifications-cron                    kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-expired-better-auth-sessions-cron         kubernetes:batch/v1:CronJob    update
~   vpc-native-update-tags-str-cron                            kubernetes:batch/v1:CronJob    update
-   vpc-native-api-clickhouse-migration-e0909e03               kubernetes:batch/v1:Job        delete
~   vpc-native-expire-super-agent-trial-cron                   kubernetes:batch/v1:CronJob    update
~   vpc-native-user-profile-analytics-clickhouse-cron          kubernetes:batch/v1:CronJob    update
+   vpc-native-api-db-migration-883ffa71                       kubernetes:batch/v1:Job        create
+   vpc-native-api-clickhouse-migration-883ffa71               kubernetes:batch/v1:Job        create
~   vpc-native-post-analytics-clickhouse-cron                  kubernetes:batch/v1:CronJob    update
~   vpc-native-rotate-daily-quests-cron                        kubernetes:batch/v1:CronJob    update
~   vpc-native-update-achievement-rarity-cron                  kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-channel-highlights-cron                   kubernetes:batch/v1:CronJob    update
~   vpc-native-hourly-notification-cron                        kubernetes:batch/v1:CronJob    update
~   vpc-native-channel-highlights-cron                         kubernetes:batch/v1:CronJob    update
~   vpc-native-deployment                                      kubernetes:apps/v1:Deployment  update
~   vpc-native-ws-deployment                                   kubernetes:apps/v1:Deployment  update
~   vpc-native-post-analytics-history-day-clickhouse-cron      kubernetes:batch/v1:CronJob    update
~   vpc-native-materialize-monthly-best-post-archives-cron     kubernetes:batch/v1:CronJob    update
~   vpc-native-bg-deployment                                   kubernetes:apps/v1:Deployment  update
~   vpc-native-user-profile-analytics-history-clickhouse-cron  kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-zombie-user-companies-cron                kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-zombie-users-cron                         kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-zombie-opportunities-cron                 kubernetes:batch/v1:CronJob    update
~   vpc-native-clean-zombie-images-cron                        kubernetes:batch/v1:CronJob    update
~   vpc-native-user-posts-analytics-refresh-cron               kubernetes:batch/v1:CronJob    update
~   vpc-native-update-tag-materialized-views-cron              kubernetes:batch/v1:CronJob    update
... and 12 other changes