Fix Claude 4 models in Vertex

[mrubens]

Important

Renamed Claude 4 model IDs in vertexModels in api.ts to use '@' instead of hyphens before the date.

• Renaming:
  • Change model IDs in vertexModels from hyphenated to '@' format for Claude 4 models.
  • Affected models: claude-sonnet-4-20250514:thinking, claude-sonnet-4-20250514, claude-opus-4-20250514:thinking, claude-opus-4-20250514.
• Files:
  • api.ts: Updated model IDs in vertexModels.

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