refactor(ai-gateway): remove retired free Tencent and LongCat models

[chrarnoldus]

Summary

• Remove the already-disabled Tencent Hy3 free and LongCat 2.0 free definitions, exclusive registrations, and Auto Free entries.
• Preserve exact-ID blocking for both retired offerings so requests and catalogs cannot expose them again; paid Tencent remains available.
• Add regression coverage for registration removal, catalog filtering, completion rejection, and endpoint metadata rejection.

Validation

• Changed-file formatting, focused oxlint, and git diff --check passed.
• Local typecheck exceeded the 120-second sandbox limit; CI typecheck passed.
• Tests were delegated to CI as requested. All applicable CI checks passed, including tests, build, lint, typecheck, and extension E2E.
• Kilo Code Review completed with no issues found. No follow-up fixes were necessary.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (10 files)

• apps/web/src/app/api/openrouter/[...path]/route.test.ts
• apps/web/src/app/api/openrouter/models/[provider]/[model]/endpoints/route.test.ts
• apps/web/src/lib/ai-gateway/models.test.ts
• apps/web/src/lib/ai-gateway/models.ts
• apps/web/src/lib/ai-gateway/providers/longcat.ts
• apps/web/src/lib/ai-gateway/providers/tencent.ts
• apps/web/src/lib/ai-gateway/unavailable-models.test.ts
• apps/web/src/lib/ai-gateway/unavailable-models.ts
• apps/web/src/tests/openrouter-models-config.test.ts
• apps/web/src/tests/openrouter-models.test.ts

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_{Reviewed by grok-4.6 · Input: 220.5K · Output: 11.9K · Cached: 231.8K}

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