Add ui elements

UI/unreal_9slice_blue/README.md

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+# Unreal 9-slice pack — BLUE variant
+
+Same geometry as the default pack:
+- Atlas **192 × 192 px**, 3×3 tiles of **64 × 64 px**
+- UE `Draw As = Box`, **Margin = 0.3333** on all sides
+- Big radius **24 px**, Small radius **12 px**
+
+Accent blue = **#4aa8ff** (Z-axis / prototype accent).
+
+## Files
+
+| File                              | Radius | Use                                  |
+| --------------------------------- | ------ | ------------------------------------ |
+| `panel_rounded_big.png`           | 24 px  | Panel — rounded (blue-tinted stroke) |
+| `panel_rounded_small.png`         | 12 px  | Panel — half-rounded                 |
+| `button_big_normal.png`           | 24 px  | Button — normal                      |
+| `button_big_hover.png`            | 24 px  | Button — hover (brighter blue edge)  |
+| `button_big_pressed.png`          | 24 px  | Button — pressed (deep, inverted)    |
+| `button_small_normal.png`         | 12 px  | Half-rounded button — normal         |
+| `button_small_hover.png`          | 12 px  | Half-rounded button — hover          |
+| `button_small_pressed.png`        | 12 px  | Half-rounded button — pressed        |
+
+`*_guide.png` files include the dashed cut lines for reference — do not ship.
+
+## Import settings (UMG)
+
+1. Texture2D → **Compression = UserInterface2D (RGBA)**, **sRGB = true**, **NoMipmaps**.
+2. Slate Brush → **Draw As = Box**, **Margin = 0.3333** on all four sides.
+3. On a `Button` widget, map the three button PNGs to Normal / Hovered / Pressed.