feat: auto-generate OpenRouter model registry from API + add missing models (#1407) (#1426)

Added scripts/generate-openrouter-models.mjs that fetches the full model
list from OpenRouter's API and generates TypeScript entries matching the
existing models.generated.ts format. Run with:
  node scripts/generate-openrouter-models.mjs > /tmp/openrouter.ts

Updated the OpenRouter section in models.generated.ts from 241 → 350
models, including all nvidia/nemotron variants requested in the issue.

Fixes #1407

Author: trek-e