provider: Add EUrouter as supported provider

[DavidLoDico]

Description:

• Add full provider integration for EUrouter
• Add provider implementation (src/providers/eurouter/)
• Register in globals.ts and providers/index.ts
• Add provider metadata to providers.json
• Add 98 supported models to models.json
• Add EUrouter logo and README table entry
• Add test configuration

EUrouter is a European AI routing API providing sovereign, GDPR-compliant access to 100+ AI models with EU data residency by default. It uses the OpenAI-compatible API format.

Why add EUrouter?

• EU data residency by default — required for GDPR compliance
• 100+ models through a single endpoint (Claude, GPT, Llama, Mistral, DeepSeek, Qwen, and more)
• OpenAI-compatible API — same format as OpenRouter
• Growing demand for European sovereign AI infrastructure

Configuration:

• Base URL: https://api.eurouter.ai/api/v1
• API Key: eur-... (get one at eurouter.ai)
• API format: OpenAI-compatible (chat/completions)

Tests Run/Test cases added:

• Build passes (npm run build)
• Prettier formatting passes
• Test variables configured for EUROUTER_API_KEY

Type of Change:

• New feature (non-breaking change which adds functionality)