feat: add GreenPT provider

[robertkeus]

Description: (required)

• Register GreenPT as an OpenAI-compatible gateway provider
• Support chat completions and embeddings at https://api.greenpt.ai/v1
• Feature flagship glm-5.2 as the chat default and green-embedding as the embedding default
• Pass through other GreenPT model IDs, including kimi-k2.7-code

GreenPT reranking and speech use provider-specific endpoints (/v1/rerank and /v1/listen) that Portkey's current OpenAI-base adapter does not expose, so this PR does not advertise unsupported operations.

Tests Run/Test cases added: (required)

• npm exec -- jest src/providers/greenpt/greenpt.test.ts --runInBand
• npm run build
• The pre-push hook built and started the gateway successfully

Type of Change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)