feat: implement chat history, theme customization, and password management

- Added chat history persistence for active rooms with auto-cleanup on stream end.
- Overhauled Settings page with user profile, theme color picker, and password change.
- Added backend API for user password updates.
- Integrated flutter_launcher_icons and updated app icon to 'H' logo.
- Fixed 'Duplicate keys' bug in danmaku by using UniqueKey and filtering historical messages.
- Updated version to 1.0.0-beta3.5 and author info.

backend/internal/api/auth.go

@@ -20,6 +20,11 @@ type LoginRequest struct {
 	Password string `json:"password" binding:"required"`
 }
 
+type ChangePasswordRequest struct {
+	OldPassword string `json:"old_password" binding:"required"`
+	NewPassword string `json:"new_password" binding:"required"`
+}
+
 func Register(c *gin.Context) {
 	var req RegisterRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
@@ -95,3 +100,40 @@ func Login(c *gin.Context) {
 		"username": user.Username,
 	})
 }
+
+func ChangePassword(c *gin.Context) {
+	userID, _ := c.Get("user_id")
+
+	var req ChangePasswordRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	var user model.User
+	if err := db.DB.First(&user, userID).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "User not found"})
+		return
+	}
+
+	// Verify old password
+	if !utils.CheckPasswordHash(req.OldPassword, user.Password) {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "Invalid old password"})
+		return
+	}
+
+	// Hash new password
+	hashedPassword, err := utils.HashPassword(req.NewPassword)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to hash password"})
+		return
+	}
+
+	// Update user
+	if err := db.DB.Model(&user).Update("password", hashedPassword).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to update password"})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"message": "Password updated successfully"})
+}