style: update various code copy button and toc styles

- Removed the old copy-action SVG icon and replaced it with a new copy-button SVG icon.
- Added a new copy-success SVG icon for visual feedback on copy actions.
- Updated Waline component comments for clarity and improved code readability.
- Enhanced BackButton component with fallback navigation to homepage.
- Improved CodeCopyButton component by refining icon handling and timeout management.
- Adjusted GithubCard component's intersection observer root margin for better visibility.
- Updated GsapAnimation component variable names for consistency and clarity.
- Removed unnecessary styles from PhotoSwipe component.
- Modified TOC component styles for better spacing and layout.
- Updated multiple theme guide markdown files to correct image hosting URL comments.
- Cleaned up extend.css by removing commented-out styles and organizing code.
- Added PhotoSwipe background color and KaTeX overflow fixes to global.css.
- Enhanced markdown.css with video styling for better responsiveness.
- Improved transition.css comments for better understanding of GSAP animation states.

src/assets/icons/copy-action.svg

@@ -1,3 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
-  <path d="M7.2 1h14.4v17.7l-1.3.5V2.5H6.7zM2.3 4.9h15.4V23H2.3zm14.1 1.5H3.6v15.1h12.8z"/>
-</svg>

src/assets/icons/copy-button.svg

@@ -1,3 +1,3 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
-  <path d="M9 20 .9 11.9l1.2-.6L9 17.6 22.5 5l.6 1z"/>
+  <path d="M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z"/>
 </svg>

src/assets/icons/copy-sucess.svg

@@ -0,0 +1,3 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+  <path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/>
+</svg>