Fix: enable chat input resizing (#12998)

## Summary
- add resizable support to shared textarea component
- enable vertical resizing for chat inputs in chat and share surfaces
- preserve autosize behavior while honoring manual resize height

## Test plan
- not run (not requested)

Fixes #12803

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Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/pages/agent/chat/box.tsx

@@ -127,6 +127,7 @@ function AgentChatBox() {
             disabled={isWaitting}
             sendDisabled={sendLoading || isWaitting}
             isUploading={loading || isWaitting}
+            resize="vertical"
             onPressEnter={handlePressEnter}
             onInputChange={handleInputChange}
             stopOutputMessage={stopOutputMessage}

web/src/pages/agent/share/index.tsx

@@ -193,6 +193,7 @@ const ChatContainer = () => {
                   value={value}
                   disabled={hasError || isWaitting}
                   sendDisabled={sendDisabled || isWaitting}
+                  resize="vertical"
                   conversationId={conversationId}
                   onInputChange={handleInputChange}
                   onPressEnter={handlePressEnter}

web/src/pages/next-chats/chat/chat-box/multiple-chat-box.tsx

@@ -255,6 +255,7 @@ export function MultipleChatBox({
           sendDisabled={sendDisabled}
           sendLoading={sendLoading}
           value={value}
+          resize="vertical"
           onInputChange={handleInputChange}
           onPressEnter={handlePressEnter}
           conversationId={conversationId}

web/src/pages/next-chats/chat/chat-box/single-chat-box.tsx

@@ -112,6 +112,7 @@ export function SingleChatBox({
         sendDisabled={sendDisabled}
         sendLoading={sendLoading}
         value={value}
+        resize="vertical"
         onInputChange={handleInputChange}
         onPressEnter={handlePressEnter}
         conversationId={conversationId}

web/src/pages/next-chats/share/index.tsx

@@ -116,6 +116,7 @@ const ChatContainer = () => {
                 value={value}
                 disabled={hasError}
                 sendDisabled={sendDisabled}
+                resize="vertical"
                 conversationId={conversationId}
                 onInputChange={handleInputChange}
                 onPressEnter={handlePressEnter}