feat: add DeepL plugin

[bensabic]

Summary

Adds DeepL plugin with the following action:

• Translate Text: Translate text with configurable target/source language, formality, and model type

Features:

• Auto-detects free vs pro API keys
• 15 target languages with regional variants
• Source language auto-detection
• Formality control
• Model type selection (quality/latency optimized)

Test plan

• Connection test validates credentials
• Actions execute successfully in a workflow
• Error handling works for invalid inputs

[vercel]

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[Copilot]

Pull request overview

This PR adds a DeepL translation plugin to the codebase, enabling text translation through DeepL's API with support for automatic detection of free vs. pro API keys, multiple target languages with regional variants, source language detection, formality control, and model type selection.

Key changes:

• Implements a complete DeepL plugin with translate-text action supporting configurable translation parameters
• Adds API key validation through DeepL's usage endpoint
• Auto-detects API key type (free vs. pro) to route requests to appropriate endpoints

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
plugins/index.ts	Registers the new deepl plugin in the plugin registry
plugins/deepl/index.ts	Defines plugin configuration, form fields, and translate-text action with language/formality/model options
plugins/deepl/test.ts	Implements API key validation using DeepL's usage endpoint
plugins/deepl/steps/translate-text.ts	Core translation logic with error handling and response parsing
plugins/deepl/icon.tsx	DeepL logo SVG component
plugins/deepl/credentials.ts	TypeScript type definition for DeepL credentials

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