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)

server/Dockerfile

@@ -1,5 +1,5 @@
 # ==========================================
-# Chat Switchboard - Backend Dockerfile
+# Switchboard Core - Backend Dockerfile
 # ==========================================
 # Standalone Go API server for cluster deployment.
 # Build context is the repo root (not ./server).