Remove Perplexity partner provider

[chrarnoldus]

Summary

• remove percentage-routed Perplexity Kimi K3 inference and managed fallback retries
• remove the partner routing configuration, admin controls, environment entry, and fallback pricing
• retain unrelated Perplexity BYOK, embeddings, and web-search support
• discard obsolete partner percentages when parsing persisted gateway configuration

Testing

• CI only, as requested

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

This PR cleanly removes the percentage-routed Perplexity partner provider; I verified that all removed symbols, config fields, and provider IDs have no remaining references and that the fallbackOnly removal does not change behavior for surviving custom-pricing models.

Files Reviewed (24 files)

• ENVIRONMENT.md
• apps/web/src/app/admin/gateway/RoutingContent.tsx
• apps/web/src/app/api/openrouter/[...path]/route.test.ts
• apps/web/src/app/api/openrouter/[...path]/route.ts
• apps/web/src/lib/ai-gateway/custom-pricing.test.ts
• apps/web/src/lib/ai-gateway/custom-pricing.ts
• apps/web/src/lib/ai-gateway/gateway-config.test.ts
• apps/web/src/lib/ai-gateway/gateway-config.ts
• apps/web/src/lib/ai-gateway/providers/apply-provider-specific-logic.test.ts
• apps/web/src/lib/ai-gateway/providers/apply-provider-specific-logic.ts
• apps/web/src/lib/ai-gateway/providers/partner/constants.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/partner/pricing.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/partner/providers.test.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/partner/providers.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/partner/routing.test.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/partner/routing.ts (deleted)
• apps/web/src/lib/ai-gateway/providers/provider-definitions.test.ts
• apps/web/src/lib/ai-gateway/providers/routing-config.ts
• apps/web/src/lib/ai-gateway/providers/routing-percentage.ts
• apps/web/src/lib/ai-gateway/providers/types.ts
• apps/web/src/lib/ai-gateway/providers/vercel/index.test.ts
• apps/web/src/lib/ai-gateway/rewriteModelResponse.test.ts
• apps/web/src/lib/ai-gateway/rewriteModelResponse.ts
• apps/web/src/routers/admin/gateway-config-router.ts

Verification Notes

• No remaining references to PERPLEXITY_KIMI_PUBLIC_ID, PERPLEXITY_KIMI_PROVIDER, partnerPricingByModelId, getPercentageRoutedPartnerProvider, PercentageRoutedPartnerInput, RoutingCohort, perplexity_routing_percentage, or DEFAULT_PERPLEXITY_PERCENTAGE anywhere in apps, packages, or services.
• KIMI_CURRENT_MODEL_ID resolves to moonshotai/kimi-k3, the same value as the deleted PERPLEXITY_KIMI_PUBLIC_ID, so the thinking-default behavior in apply-provider-specific-logic.ts:223 is unchanged.
• CustomPricing.fallbackOnly had no remaining producers after partner pricing was deleted, so the simplified checks in custom-pricing.ts and rewriteModelResponse.ts:937 are behavior-preserving. processUsage.ts:1207 reads the separate KiloExclusivePricing.fallbackOnly, unaffected by this change.
• Removed after(...), clone(), and body.cancel() fallback code does not introduce memory leaks; after and GatewayRequest remain used elsewhere in route.ts.
• PERPLEXITY_API_KEY had no remaining code or dotenv references, so the ENVIRONMENT.md removal is consistent, while BYOK, embedding, and web-search Perplexity usages are unrelated and retained.

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