Refactor toast notifications and modal dialog implementation

- Updated SCSS for toast notifications to support multiple toast types (success, info, warning, error) and improved layout.
- Added new SVG icons for error, info, success, and warning notifications.
- Created separate HTML templates for toast notifications and modal dialogs.
- Enhanced the dev panel with buttons to test different toast notifications and modal dialogs.

backend/static/error.svg

@@ -0,0 +1,54 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   width="40.905399mm"
+   height="40.905399mm"
+   viewBox="0 0 40.905399 40.905399"
+   version="1.1"
+   id="svg1"
+   sodipodi:docname="error.svg"
+   inkscape:version="1.4 (86a8ad7, 2024-10-11)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <sodipodi:namedview
+     id="namedview1"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="0.0"
+     inkscape:pagecheckerboard="true"
+     inkscape:deskcolor="#d1d1d1"
+     inkscape:document-units="mm"
+     inkscape:zoom="1.4702524"
+     inkscape:cx="-96.582055"
+     inkscape:cy="13.263029"
+     inkscape:window-width="2560"
+     inkscape:window-height="1369"
+     inkscape:window-x="-8"
+     inkscape:window-y="828"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="layer1" />
+  <defs
+     id="defs1" />
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(-80.178404,-120.49168)">
+    <circle
+       style="fill:#ff1e1e;fill-opacity:1;stroke:#a00000;stroke-width:7;stroke-linecap:butt;stroke-linejoin:bevel;stroke-dasharray:none;stroke-opacity:1;paint-order:stroke fill markers"
+       id="path2"
+       cx="100.6311"
+       cy="140.94438"
+       r="16.9527" />
+    <path
+       d="m 107.32373,131.05185 -6.61942,6.62988 q -0.0732,0.0628 -0.13595,0 l -6.629879,-6.62988 q -0.658805,-0.6588 -1.599955,-0.6588 -0.930694,0 -1.589499,0.6588 -0.669262,0.66926 -0.669262,1.61042 0,0.93069 0.669262,1.58949 l 6.619425,6.62989 q 0.0732,0.0627 0,0.12548 l -6.619425,6.62988 q -0.669262,0.65881 -0.669262,1.5895 0,0.94115 0.669262,1.61042 0.658805,0.6588 1.589499,0.6588 0.94115,0 1.599955,-0.6588 l 6.629879,-6.62989 q 0.0628,-0.0627 0.13595,0 l 6.61942,6.62989 q 0.65881,0.6588 1.59996,0.6588 0.94115,0 1.59995,-0.6588 0.65881,-0.66927 0.65881,-1.61042 0,-0.93069 -0.65881,-1.5895 l -6.62988,-6.62988 q -0.0627,-0.0627 0,-0.12548 l 6.62988,-6.62989 q 0.65881,-0.6588 0.65881,-1.58949 0,-0.94116 -0.65881,-1.61042 -0.6588,-0.6588 -1.59995,-0.6588 -0.94115,0 -1.59996,0.6588 z"
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+  </g>
+</svg>