step 1: rename module chat-switchboard → switchboard-core

- go.mod module name
- All 714 import references across 289 Go files
- VERSION: 0.1.0
- CI DB names: switchboard_core_{ci,dev,test}
- Docker image: gobha/switchboard-core
- Test fixtures: JWT issuer, repo names
- .env.example, docker-compose container name
- Compiles clean (go build exit 0)

Dockerfile

@@ -1,5 +1,5 @@
 # ============================================
-# Chat Switchboard — Unified Dockerfile
+# Switchboard Core — Unified Dockerfile
 # ============================================
 # Stage 1: Build Go backend
 # Stage 2: Download JS vendor libs (marked, DOMPurify)