feat: add gRPC-Web client service layer for OrchestratorService

- Create src/lib/services/orchestrator.ts with Connect-Web transport
- Typed processRequest() async generator for server-streaming RPC
- OrchestratorError class mapping gRPC status codes to app errors
- Configurable endpoint with resetTransport() for reconfiguration

Closes #4

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/services/orchestrator.ts

@@ -0,0 +1,89 @@
+import { createClient } from '@connectrpc/connect';
+import { createGrpcWebTransport } from '@connectrpc/connect-web';
+import { OrchestratorService } from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+import type {
+	ProcessRequestResponse,
+	SessionConfig
+} from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+import { create } from '@bufbuild/protobuf';
+import { ProcessRequestRequestSchema } from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+
+/**
+ * Application-level error wrapping gRPC status codes.
+ */
+export class OrchestratorError extends Error {
+	constructor(
+		message: string,
+		public readonly code: string,
+		public readonly details?: string
+	) {
+		super(message);
+		this.name = 'OrchestratorError';
+	}
+}
+
+const DEFAULT_ENDPOINT = '/';
+
+let transport: ReturnType<typeof createGrpcWebTransport> | null = null;
+
+function getTransport(endpoint?: string) {
+	if (!transport) {
+		transport = createGrpcWebTransport({
+			baseUrl: endpoint ?? DEFAULT_ENDPOINT
+		});
+	}
+	return transport;
+}
+
+/**
+ * Reset the transport (useful for reconfiguring the endpoint).
+ */
+export function resetTransport(): void {
+	transport = null;
+}
+
+/**
+ * Create a configured orchestrator client.
+ */
+function getClient(endpoint?: string) {
+	return createClient(OrchestratorService, getTransport(endpoint));
+}
+
+/**
+ * Send a request to the orchestrator and yield streaming responses.
+ *
+ * Returns an async iterator of `ProcessRequestResponse` messages,
+ * each containing the current orchestration state, status message,
+ * and optionally intermediate or final results.
+ */
+export async function* processRequest(
+	sessionId: string,
+	userMessage: string,
+	sessionConfig?: SessionConfig,
+	endpoint?: string
+): AsyncGenerator<ProcessRequestResponse> {
+	const client = getClient(endpoint);
+
+	const request = create(ProcessRequestRequestSchema, {
+		sessionId,
+		userMessage,
+		sessionConfig
+	});
+
+	try {
+		for await (const response of client.processRequest(request)) {
+			yield response;
+		}
+	} catch (err: unknown) {
+		if (err instanceof Error) {
+			// ConnectError has a `code` property
+			const code = 'code' in err ? (err as { code: unknown }).code : undefined;
+			throw new OrchestratorError(
+				err.message,
+				typeof code === 'string' ? code : 'unknown',
+				err.message
+			);
+		}
+		throw new OrchestratorError('Unknown error', 'unknown');
+	}
+}