feat: Add openRouter integration

[harxhist]

Closes #3205

Description

This PR adds the OpenRouter integration to SuperPlane, so users can use a single API key to call many LLM providers (OpenAI, Anthropic, Google, etc.) via OpenRouter’s unified API.

It includes the base integration and three components:

• Text Prompt (Action): Calls OpenRouter’s chat completions API with a user prompt and optional system message and returns a single assistant reply. Config: Model (required), Prompt (required), System message, Max tokens, Temperature. Output: id, model, text, usage, finishReason. Use cases: run summaries, PR analysis, incident summaries, docs.
• Get Remaining Credits (Action): Returns total credits purchased and used for the account. No config; uses the base API key. Management API key required (standard keys get 403). Output: totalCredits, totalUsage, remaining. Use cases: cost tracking, low-credit alerts.
• Get Current Key Details (Action): Returns key metadata for the authenticated API key. No config. Output: label, usage, usageDaily / usageWeekly / usageMonthly, limit, limitRemaining, limitReset, isFreeTier, isManagementKey, expiresAt (if any). Use cases: usage reporting, limit checks.

Implementation Notes

• Authentication: API key in header Authorization: Bearer <key>. Requests go to https://openrouter.ai/api/v1/.
• Model picker: Optional model resource type backed by GET /models for the Text Prompt component.
• No OAuth or webhooks.

Loom Video

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have signed off my commits (git commit -s)

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