Revert "fix(cost-insights): decouple usage rollups and gate plan suggestions"

[jeanduplessis]

Reverts #4588

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Verified this is a byte-perfect revert of #4588 (confirmed the full repo tree at the revert commit is identical to the pre-#4588 baseline), so no new bugs, security issues, or migration inconsistencies are introduced.

Files Reviewed (16 files)

• apps/web/src/app/api/cron/cost-insights-hourly/route.test.ts
• apps/web/src/app/api/cron/cost-insights-hourly/route.ts
• apps/web/src/lib/ai-gateway/processUsage.test.ts
• apps/web/src/lib/ai-gateway/processUsage.ts
• apps/web/src/lib/ai-gateway/usage-daily-rollup-repairs.test.ts (deleted)
• apps/web/src/lib/ai-gateway/usage-daily-rollup-repairs.ts (deleted)
• apps/web/src/lib/coding-plans/index.test.ts
• apps/web/src/lib/coding-plans/pricing.ts
• apps/web/src/lib/cost-insights/evaluation.ts
• apps/web/src/lib/cost-insights/jobs.ts
• apps/web/src/lib/cost-insights/suggestion-eligibility.test.ts (deleted)
• apps/web/src/lib/cost-insights/suggestion-eligibility.ts (deleted)
• dev/seed/cost-insights/spend-evidence.ts
• packages/db/src/migrations/0188_unusual_titanium_man.sql (deleted)
• packages/db/src/migrations/meta/_journal.json (generated, skipped per review rules)
• packages/db/src/schema.ts

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_{Review guidance: REVIEW.md from base branch main}