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/_index.md

@@ -5,3 +5,4 @@
 | #1    | Project scaffolding: SvelteKit + Tailwind + TypeScript | COMPLETED    | [issue-001.md](issue-001.md) |
 | #2    | Proto codegen pipeline for TypeScript gRPC-Web stubs   | COMPLETED    | [issue-002.md](issue-002.md) |
 | #3    | Configure Caddy for gRPC-Web support                   | COMPLETED    | [issue-003.md](issue-003.md) |
+| #4    | gRPC-Web client service layer                          | COMPLETED    | [issue-004.md](issue-004.md) |

implementation-plans/issue-004.md

@@ -0,0 +1,25 @@
+---
+---
+
+# 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.