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

web/app/dashboard/conversations/_components/chat-panel.tsx

@@ -343,7 +343,7 @@ export function ChatPanel() {
   const messagesScroll = (
     <div
       ref={messagesContainerRef}
-      className="h-full min-h-0 flex-1 overflow-y-auto p-4 cs-agent-scrollbar"
+      className="h-full min-h-0 flex-1 overflow-y-auto p-4 bosschat-scrollbar"
     >
       <div ref={messagesContentRef} className="flex flex-col">
         {!loading && messages.length > 0 && messagesHasMore ? (