Make SettingsForm resizable with scrollbars

[Copilot]

The SettingsForm window was previously fixed-size (FormBorderStyle.FixedDialog), preventing users from adjusting the window size or scrolling when content exceeded viewport dimensions.

Changes

• Form properties: Changed FormBorderStyle to Sizable, enabled MaximizeBox, added MinimumSize constraint (650x550), and enabled AutoScroll
• Layout anchors: Added proper Anchor styles to TabControl (expand with window) and dialog buttons (stay bottom-right)

// Before: Fixed dialog
this.FormBorderStyle = FormBorderStyle.FixedDialog;
this.MaximizeBox = false;

// After: Resizable with scrollbars
this.FormBorderStyle = FormBorderStyle.Sizable;
this.MaximizeBox = true;
this.MinimumSize = new Size(650, 550);
this.AutoScroll = true;

_tabControl = new TabControl {
    Anchor = AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Left | AnchorStyles.Right
};

Scrollbars appear automatically when window is smaller than content. Implementation follows existing pattern in ChatForm.cs.

Original prompt

The main windows needs to be resizable and have scroll bars for pages that exceed the length of the window.

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