feat: add Nebius AI as codebase indexing provider

- Add NebiusEmbedder implementation using OpenAI-compatible API
- Support Qwen/Qwen3-Embedding-8B model with 4096 dimensions
- Add configuration UI and settings management
- Include comprehensive test coverage
- Update all type definitions and interfaces
- Add i18n translations for Nebius-related messages
- Implement batching and rate limiting for embeddings
- Use base64 encoding for large dimension arrays

Closes #8589

src/core/webview/webviewMessageHandler.ts

@@ -2647,6 +2647,7 @@ export const webviewMessageHandler = async (
 					hasGeminiApiKey,
 					hasMistralApiKey,
 					hasVercelAiGatewayApiKey,
+					hasNebiusApiKey,
 				},
 			})
 			break

src/shared/WebviewMessage.ts

@@ -288,6 +288,7 @@ export interface WebviewMessage {
 			| "gemini"
 			| "mistral"
 			| "vercel-ai-gateway"
+			| "nebius"
 		codebaseIndexEmbedderBaseUrl?: string
 		codebaseIndexEmbedderModelId: string
 		codebaseIndexEmbedderModelDimension?: number // Generic dimension for all providers
@@ -302,6 +303,7 @@ export interface WebviewMessage {
 		codebaseIndexGeminiApiKey?: string
 		codebaseIndexMistralApiKey?: string
 		codebaseIndexVercelAiGatewayApiKey?: string
+		codebaseIndexNebiusApiKey?: string
 	}
 }