feat: Add ModelsLab provider for image generation

[adhikjoshi]

Summary

Adds ModelsLab as a new AI provider for image generation (text-to-image) via the Portkey AI Gateway.

ModelsLab is a developer-first AI API platform offering 200+ models for image, video, voice, and 3D generation. It currently routes to providers like Stability AI, FLUX, SDXL, and thousands of community fine-tuned models.

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What this PR adds

File	Purpose
src/providers/modelslab/api.ts	Base URL, headers, endpoint routing
src/providers/modelslab/imageGenerate.ts	ProviderConfig + response transform
src/providers/modelslab/index.ts	Provider config registry
src/globals.ts	MODELSLAB provider constant
src/providers/index.ts	Register modelslab in provider map

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Parameter Mapping

Portkey param	ModelsLab param	Notes
prompt	prompt	Required
model	model_id	Default: flux
n	samples	1–4
size (e.g. 1024x1024)	width, height	Min 256px
steps	num_inference_steps	1–50, default 30
guidance_scale	guidance_scale	1–20, default 7.5
seed	seed
negative_prompt	negative_prompt

Auth: ModelsLab uses key-in-body authentication. The API key from providerOptions.apiKey is automatically injected into the request body as "key".

Async/Webhook: For slow models, ModelsLab returns "status": "processing" with a fetch_result poll URL. This provider surfaces that as an error message with the poll URL; consumers should use the webhook parameter for async workflows.

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Usage

curl http://localhost:8787/v1/images/generations \
  -H 'Content-Type: application/json' \
  -H 'x-portkey-provider: modelslab' \
  -H 'Authorization: Bearer YOUR_MODELSLAB_API_KEY' \
  -d '{
    "prompt": "a photorealistic sunset over mountain peaks",
    "model": "flux",
    "n": 1,
    "size": "1024x1024"
  }'

Response:

{
  "created": 1708512345,
  "data": [
    { "url": "https://...modelslab.com/.../output.png" }
  ]
}

---

API Reference

• Docs: https://docs.modelslab.com
• Image generation: https://docs.modelslab.com/image-generation/community-models/text2img
• Get API key: https://modelslab.com/dashboard/api-keys

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Checklist

• Follows existing provider file structure (api.ts / imageGenerate.ts / index.ts)
• Added provider constant to globals.ts
• Registered in providers/index.ts
• TypeScript compiles (no new errors)
• Prettier check passes
• Build succeeds (rollup -c)

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