feat: Implement Share Modal for document sharing functionality

- Added ShareModal component to manage user and link sharing for documents.
- Created AuthContext to handle user authentication state and token management.
- Updated useYjsDocument hook to support sharing via tokens.
- Enhanced Yjs document creation to include user information and authentication tokens.
- Introduced AuthCallback page to handle authentication redirects and token processing.
- Modified EditorPage and KanbanPage to include share functionality.
- Created LoginPage with Google and GitHub authentication options.
- Added styles for LoginPage.
- Defined types for authentication and sharing in respective TypeScript files.

backend/internal/hub/yjs_protocol.go

@@ -0,0 +1,99 @@
+package hub
+
+import (
+	"encoding/binary"
+)
+
+// 这个函数用来从前端发来的二进制数据里，提取出 Yjs 的 ClientID 和对应的 Clock
+// data: 前端发来的 []byte
+// return: map[clientID]clock
+func SniffYjsClientIDs(data []byte) map[uint64]uint64 {
+    // 简单的防御：如果不是 Type 1 (Awareness) 消息，直接忽略
+    if len(data) < 2 || data[0] != 1 {
+        return nil
+    }
+
+    result := make(map[uint64]uint64)
+    offset := 1 // 跳过 [0] MessageType
+
+    // 读取总长度 (跳过)
+    _, n := binary.Uvarint(data[offset:])
+    if n <= 0 { return nil }
+    offset += n
+
+    // 读取 Count (包含几个客户端的信息)
+    count, n := binary.Uvarint(data[offset:])
+    if n <= 0 { return nil }
+    offset += n
+
+    // 循环读取每个客户端的信息
+    for i := 0; i < int(count); i++ {
+        if offset >= len(data) { break }
+
+        // 1. 读取 ClientID
+        id, n := binary.Uvarint(data[offset:])
+        if n <= 0 { break }
+        offset += n
+
+        // 2. 读取 Clock (现在我们需要保存它！)
+        clock, n := binary.Uvarint(data[offset:])
+        if n <= 0 { break }
+        offset += n
+
+        // 保存 clientID -> clock
+        result[id] = clock
+
+        // 3. 跳过 JSON String
+        if offset >= len(data) { break }
+        strLen, n := binary.Uvarint(data[offset:])
+        if n <= 0 { break }
+        offset += n
+
+        // 跳过具体字符串内容
+        offset += int(strLen)
+    }
+
+    return result
+}
+
+// 这个函数用来伪造一条"删除消息"
+// 输入：clientClocks map[clientID]clock - 要删除的 ClientID 及其最后已知的 clock 值
+// 输出：可以广播给前端的 []byte
+func MakeYjsDeleteMessage(clientClocks map[uint64]uint64) []byte {
+    if len(clientClocks) == 0 {
+        return nil
+    }
+
+    // 构造 Payload (负载)
+    // 格式: [Count] [ID] [Clock] [StringLen] [String] ...
+    payload := make([]byte, 0)
+
+    // 写入 Count (变长整数)
+    buf := make([]byte, 10)
+    n := binary.PutUvarint(buf, uint64(len(clientClocks)))
+    payload = append(payload, buf[:n]...)
+
+    for id, clock := range clientClocks {
+        // ClientID
+        n = binary.PutUvarint(buf, id)
+        payload = append(payload, buf[:n]...)
+        // Clock: 必须使用 clock + 1，这样 Yjs 才会接受这个更新！
+        n = binary.PutUvarint(buf, clock+1)
+        payload = append(payload, buf[:n]...)
+        // String Length (填 4，因为 "null" 长度是 4)
+        n = binary.PutUvarint(buf, 4)
+        payload = append(payload, buf[:n]...)
+        // String Content (这里是关键：null 代表删除用户)
+        payload = append(payload, []byte("null")...)
+    }
+
+    // 构造最终消息: [Type=1] [PayloadLength] [Payload]
+    finalMsg := make([]byte, 0)
+    finalMsg = append(finalMsg, 1) // Type 1
+
+    n = binary.PutUvarint(buf, uint64(len(payload)))
+    finalMsg = append(finalMsg, buf[:n]...) // Length
+    finalMsg = append(finalMsg, payload...) // Body
+
+    return finalMsg
+}