fix(ui): wire drag-and-drop file upload in chat view

Lift file state from ChatInput to ChatPage so DropZone.onDrop can
append dropped files to the shared state. Previously drag-and-drop
showed the overlay but never passed files to the input.

ui/web/src/components/chat/chat-input.tsx

@@ -14,12 +14,13 @@ interface ChatInputProps {
   onAbort: () => void;
   isRunning: boolean;
   disabled?: boolean;
+  files: AttachedFile[];
+  onFilesChange: (files: AttachedFile[]) => void;
 }
 
-export function ChatInput({ onSend, onAbort, isRunning, disabled }: ChatInputProps) {
+export function ChatInput({ onSend, onAbort, isRunning, disabled, files, onFilesChange }: ChatInputProps) {
   const { t } = useTranslation("common");
   const [value, setValue] = useState("");
-  const [files, setFiles] = useState<AttachedFile[]>([]);
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const fileInputRef = useRef<HTMLInputElement>(null);
 
@@ -27,11 +28,11 @@ export function ChatInput({ onSend, onAbort, isRunning, disabled }: ChatInputPro
     if ((!value.trim() && files.length === 0) || disabled) return;
     onSend(value, files.length > 0 ? files : undefined);
     setValue("");
-    setFiles([]);
+    onFilesChange([]);
     if (textareaRef.current) {
       textareaRef.current.style.height = "auto";
     }
-  }, [value, files, onSend, disabled]);
+  }, [value, files, onSend, onFilesChange, disabled]);
 
   const handleKeyDown = useCallback(
     (e: KeyboardEvent<HTMLTextAreaElement>) => {
@@ -58,14 +59,14 @@ export function ChatInput({ onSend, onAbort, isRunning, disabled }: ChatInputPro
     const selected = e.target.files;
     if (!selected) return;
     const newFiles: AttachedFile[] = Array.from(selected).map((f) => ({ file: f }));
-    setFiles((prev) => [...prev, ...newFiles]);
+    onFilesChange([...files, ...newFiles]);
     // Reset input so the same file can be re-selected
     e.target.value = "";
-  }, []);
+  }, [files, onFilesChange]);
 
   const removeFile = useCallback((index: number) => {
-    setFiles((prev) => prev.filter((_, i) => i !== index));
-  }, []);
+    onFilesChange(files.filter((_, i) => i !== index));
+  }, [files, onFilesChange]);
 
   return (
     <div

ui/web/src/pages/chat/chat-page.tsx

@@ -24,6 +24,7 @@ export function ChatPage() {
   const userId = useAuthStore((s) => s.userId);
 
   const [scrollTrigger, setScrollTrigger] = useState(0);
+  const [files, setFiles] = useState<AttachedFile[]>([]);
 
   // sessionKey derived from URL — single source of truth, no separate state
   const sessionKey = urlSessionKey ?? "";
@@ -118,18 +119,22 @@ export function ChatPage() {
   );
 
   const handleSend = useCallback(
-    (message: string, files?: AttachedFile[]) => {
+    (message: string, sendFiles?: AttachedFile[]) => {
       let key = sessionKey;
       if (!key) {
         key = buildNewSessionKey();
         navigate(`/chat/${encodeURIComponent(key)}`, { replace: true });
       }
-      send(message, key, files);
+      send(message, key, sendFiles);
       setScrollTrigger((n) => n + 1);
     },
     [sessionKey, send, buildNewSessionKey, navigate],
   );
 
+  const handleDropFiles = useCallback((dropped: File[]) => {
+    setFiles((prev) => [...prev, ...dropped.map((f) => ({ file: f }))]);
+  }, []);
+
   const handleAbort = useCallback(() => {
     abort(sessionKey);
   }, [abort, sessionKey]);
@@ -215,7 +220,7 @@ export function ChatPage() {
           </div>
         )}
 
-        <DropZone onDrop={() => { /* TODO: wire to chat input */ }}>
+        <DropZone onDrop={handleDropFiles}>
           <ChatThread
             messages={messages}
             streamText={streamText}
@@ -235,6 +240,8 @@ export function ChatPage() {
               onAbort={handleAbort}
               isRunning={isRunning}
               disabled={!connected}
+              files={files}
+              onFilesChange={setFiles}
             />
           ) : (
             <div className="mx-3 mb-3 flex items-center gap-2 rounded-xl border bg-muted/50 px-4 py-3 text-sm text-muted-foreground shadow-sm">