Add cursor shader

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+# Cursor shaders for ghostty
+## WARNING: These are extremely customizable
+
+## Demos
+
+| Effect                              | Demo                                                                                                 |
+| --------                            | ------                                                                                               |
+| Cursor Warp<br>(Neovide-like)       | ![cursor_warp](https://github.com/user-attachments/assets/5323330c-e09d-4d80-963b-f0cb8413cac9)      |
+| Cursor Sweep                        | ![cursor_sweep](https://github.com/user-attachments/assets/c8979569-e0fa-48f1-afd7-9eed36df7f0a)     |
+| Cursor Tail<br>(Kitty-like)         | ![cursor_tail](https://github.com/user-attachments/assets/0c1ecd67-8ff4-4198-9e89-a4435289bfa0)      |
+| Ripple Cursor                       | ![ripple_cursor](https://github.com/user-attachments/assets/e489f74e-620a-490a-b5c5-d3918a5077c1)    |
+| Sonic Boom                          | ![sonic_boom](https://github.com/user-attachments/assets/91ac80e6-aa2b-41a3-8b49-d674ce287709)       |
+| Ripple Rectangle                    | ![ripple_rectangle](https://github.com/user-attachments/assets/5c8028eb-6ffb-4e38-a5dd-e2c0ed6a4175) |
+| Customized<br>(faded warp + ripple) | ![customized_warp](https://github.com/user-attachments/assets/3be0d82e-2bff-48ab-824e-3262cbb10d4d)  |
+
+## Trails
+- [cursor_warp.glsl](cursor_warp.glsl): Neovide-like cursor trail, most customizable shader
+- [cursor_sweep.glsl](cursor_sweep.glsl): Animated trail that shrinks from previous to current cursor position
+- [cursor_tail.glsl](cursor_tail.glsl): Comet-like trail, mimicing kitty terminal's cursor_trail effect
+
+## Pulse/Boom effects
+- These trigger on cursor mode changes (block to line or vice versa, looks cool on changing modes in vim)
+- [sonic_boom_cursor.glsl](sonic_boom_cursor.glsl): expanding filled circle 
+- [ripple_cursor.glsl](ripple_cursor.glsl): Expanding circular ring ripple effect
+- [rectangle_boom_cursor.glsl](rectangle_boom_cursor.glsl): Same as boom_cursor but rectangular(cursor shape)
+- [ripple_rectangle_cursor.glsl](ripple_rectangle_cursor.glsl): Same as ripple_cursor but rectangular(cursor shape)
+
+
+> [!NOTE]
+> If you have the line cursor (default), these effects will trigger and freeze on unfocus(as cursor changes to hollow block). The solution is to add `custom-shader-animation = always` to your ghostty config
+
+## Usage
+
+1. Clone the repo into your ghostty shaders directory:
+```bash
+git clone https://github.com/sahaj-b/ghostty-cursor-shaders ~/.config/ghostty/shaders
+```
+
+2. In your `~/.config/ghostty/config`, add:
+```config
+custom-shader = shaders/yourshader1.glsl
+custom-shader = shaders/yourshader2.glsl
+# ...
+```
+Replace `yourshader` with the name of any shader file (e.g., `cursor_sweep`, `ripple_cursor`, etc.)
+
+
+## Customization
+- All shaders has customizable parameters (like color, duration, size, thickness, etc) etc at the top of each file. You can adjust
+- Also, all files has various **Easing Functions** to choose from.
+  - these function control the animation curve of the effects, you can make them elasitcy, springy, smooth, linear, etc by changing the easing function
+  - in trail shaders, you can comment/uncomment the easing functions in the code
+  - in pulse/boom shaders, you can comment/uncomment the lines in the `ANIMATION` section
+  - you can also add your own easing functions if you want
+
+### Example (faded warp + ripple)
+```glsl
+// in cursor_warp.glsl
+const float DURATION = 0.15;
+const float TRAIL_SIZE = 0.8;
+const float THRESHOLD_MIN_DISTANCE = 1.0;
+const float BLUR = 1.0;
+const float TRAIL_THICKNESS = 1.0;
+const float TRAIL_THICKNESS_X = 0.9;
+
+const float FADE_ENABLED = 1.0;
+const float FADE_EXPONENT = 5.0;
+```
+```glsl
+// in ripple_cursor.glsl
+const float DURATION = 0.15;
+const float MAX_RADIUS = 0.026;
+const float RING_THICKNESS = 0.02;
+const float CURSOR_WIDTH_CHANGE_THRESHOLD = 0.5;
+vec4 COLOR = vec4(0.35, 0.36, 0.44, 0.8);
+const float BLUR = 3.5;
+const float ANIMATION_START_OFFSET = 0.01;
+```
+
+## Acknowledgements
+Inspired by [Neovide](https://neovide.dev/) cursor animations and [KroneCorylus/ghostty-shader-playground](https://github.com/KroneCorylus/ghostty-shader-playground)
+
+## License
+MIT
+
+## Why use branching(if/else) instead of branchless math
+- coz we are dealing with **uniform branching** here, which has **NO DIVERGENCE**.
+- ie, all fragments will take the same branch path, so no performance penalty on modern GPUs
+- Branchless math would force GPU to calculate animations every single frame, even when there is no need