refactor: rebrand from cs-agent to BossChat

- Rename Go module: cs-agent → bosschat
- Rename all import paths across 200+ Go files
- Rename SDK: cs-ai-agent-sdk → bosschat-sdk
- Rename message protocol: cs-agent:* → bosschat:*
- Rename JS globals: CSAgentConfig → BossChatConfig
- Rename CSS classes: cs-agent-* → bosschat-*
- Update Makefile APP_NAME and ARCHIVE_NAME
- Update logo assets
- Fix display name: BoosChat → BossChat

internal/pkg/dto/response/asset_response.go

@@ -1,6 +1,6 @@
 package response
 
-import "cs-agent/internal/pkg/enums"
+import "bosschat/internal/pkg/enums"
 
 type AssetResponse struct {
 	ID             int64               `json:"id"`