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>

implementation-plans/issue-004.md

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+---
+---
+
+# Issue #4: gRPC-Web client service layer
+
+**Status:** COMPLETED
+**Issue:** https://git.shahondin1624.de/llm-multiverse/llm-multiverse-ui/issues/4
+**Branch:** `feature/issue-4-grpc-web-client`
+
+## Summary
+
+Create `src/lib/services/orchestrator.ts` wrapping Connect-Web client for the OrchestratorService, with typed `processRequest()` async generator and error mapping.
+
+## Acceptance Criteria
+
+- [x] `src/lib/services/orchestrator.ts` module created
+- [x] Wraps generated gRPC-Web stubs with typed interface
+- [x] Connection setup with configurable endpoint
+- [x] Error mapping from gRPC status codes to application errors
+- [x] `processRequest()` returns an async iterator of `ProcessRequestResponse`
+- [x] Handles streaming responses correctly
+
+## Deviations
+
+None.