Remove blank space from dataset and generative layout

[Irozuku]

This pull request refactors the layout and styling of several components in the generative and datasets modules to improve consistency and modularity. The main changes include introducing a reusable SideBar component for left and right navigation bars, standardizing header and button layouts, and simplifying container styling across pages. These updates enhance the user interface's visual coherence and maintainability.

Layout and Component Refactoring

• Introduced a reusable SideBar component, replacing previous sidebar implementations in ParamsBar, SessionBar, and LeftBar for consistent sidebar structure and styling.

• Updated page layouts to use the new sidebar and center box components, removing unnecessary padding and margin, and ensuring consistent width allocations for sidebar, center, and right bar sections in generative and datasets pages.
  Header and Button Standardization

• Standardized header sections in sidebars and right bars to use a fixed height and consistent typography, and improved the appearance and behavior of the "New Item" button for sidebar headers.

Styling and Usability Improvements

• Improved sidebar and center box styling by adjusting border thickness, removing rounded corners, and standardizing background and border colors for better visual alignment.
• Enhanced usability in parameter editing by adding a sticky submit button and a placeholder message when no session is selected.