fix: async document processing in background threads, improve chat UX

- Fix knowledge_base_service calling async process_document synchronously
  in background threads — use asyncio.new_event_loop().run_until_complete()
  instead of bare call that returned unawaited coroutine
- Same fix for _update_document and reindex_document
- Replace ModeSelector with auto-detect: RAG mode when knowledge bases selected
- Convert regenerateMessage to streaming (was synchronous API call)
- Show "知识库检索模式" indicator above input when KB selected
- Remove loadSessions side-effect from streaming onComplete
- Fix chat page loading state to avoid flash
- Improve forum page spacing and sizing

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/components/chat/chat-interface.tsx

@@ -4,10 +4,9 @@ import { useState, useRef, useEffect } from "react";
 import { useChatStore } from "@/store/chat";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
-import { Send, Square, Bot, ChevronDown, Settings2 } from "lucide-react";
+import { Send, Square, Bot, ChevronDown, Settings2, Database } from "lucide-react";
 import MessageList from "./message-list";
 import QuickQuestions from "./quick-questions";
-import ModeSelector, { ChatMode } from "./mode-selector";
 import ModelSelector from "./model-selector";
 import KnowledgeSelector, { KnowledgeBase } from "./knowledge-selector";
 import { cn } from "@/lib/utils";
@@ -16,7 +15,6 @@ import { knowledgeBaseAPI } from "@/lib/api";
 export default function ChatInterface() {
   const [inputMessage, setInputMessage] = useState("");
   const [isComposing, setIsComposing] = useState(false);
-  const [chatMode, setChatMode] = useState<ChatMode>("normal");
   const [selectedModel, setSelectedModel] = useState("deepseek-ai/DeepSeek-V3");
   const [selectedKnowledgeBases, setSelectedKnowledgeBases] = useState<string[]>([]);
   const [systemKnowledgeBases, setSystemKnowledgeBases] = useState<KnowledgeBase[]>([]);
@@ -72,7 +70,8 @@ export default function ChatInterface() {
         await selectSession(newSession.id);
       }
     }
-    await streamMessage(message, chatMode, selectedKnowledgeBases, selectedModel);
+    const mode = selectedKnowledgeBases.length > 0 ? "rag" : "normal";
+    await streamMessage(message, mode, selectedKnowledgeBases, selectedModel);
   };
 
   const handleKeyPress = (e: React.KeyboardEvent) => {
@@ -124,7 +123,6 @@ export default function ChatInterface() {
         {/* Settings panel — collapsible */}
         {showSettings && (
           <div className="flex items-center gap-2 mb-3 pb-3 border-b border-border/30">
-            <ModeSelector mode={chatMode} onModeChange={setChatMode} />
             <ModelSelector
               selectedModel={selectedModel}
               onModelChange={setSelectedModel}
@@ -156,6 +154,12 @@ export default function ChatInterface() {
           </Button>
 
           <div className="flex-1 relative">
+            {selectedKnowledgeBases.length > 0 && (
+              <div className="absolute -top-0.5 left-3 right-3 flex items-center gap-1 text-[10px] text-primary font-medium pointer-events-none">
+                <Database className="w-3 h-3" />
+                <span>知识库检索模式</span>
+              </div>
+            )}
             <input
               ref={inputRef}
               value={inputMessage}
@@ -167,6 +171,7 @@ export default function ChatInterface() {
               disabled={isLoading || isStreaming}
               className={cn(
                 "w-full h-10 px-4 rounded-xl text-sm",
+                selectedKnowledgeBases.length > 0 && "pt-4",
                 "bg-muted/40 border border-border/30",
                 "placeholder:text-muted-foreground/60",
                 "focus:outline-none focus:ring-2 focus:ring-primary/20 focus:border-primary/30",