docs: refine README layout per feedback

- Move banner image to very top, remove feature background images
- Move product screenshot into "What is Multica?" section
- Fix logo SVG: use icon-only (no text) for reliable GitHub rendering
- Use markdown heading for "Multica" text instead of SVG text element
- Clean up features into a single bullet list

docs/assets/logo-dark.svg

@@ -1,8 +1,7 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 400 100" role="img" aria-label="Multica">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 80 80" role="img" aria-label="Multica">
   <polygon
     fill="#f9fafb"
-    points="25,51.1 25,80 35,80 35,51.1 61.8,77.9 68.9,70.8 42.1,44 80,44 80,34 42.1,34 68.9,7.2 61.8,0.1 35,26.9 35,-11 25,-11 25,26.9 -1.8,0.1 -8.9,7.2 17.9,34 -20,34 -20,44 17.9,44 -8.9,70.8 -1.8,77.9"
-    transform="translate(30, 20) scale(0.75)"
+    points="35,51.1 35,80 45,80 45,51.1 71.8,77.9 78.9,70.8 52.1,44 90,44 90,34 52.1,34 78.9,7.2 71.8,0.1 45,26.9 45,-11 35,-11 35,26.9 8.2,0.1 1.1,7.2 27.9,34 -10,34 -10,44 27.9,44 1.1,70.8 8.2,77.9"
+    transform="translate(5, 5.5) scale(0.87)"
   />
-  <text x="95" y="62" font-family="-apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif" font-size="48" font-weight="700" fill="#f9fafb" letter-spacing="-1">Multica</text>
 </svg>

docs/assets/logo-light.svg

@@ -1,8 +1,7 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 400 100" role="img" aria-label="Multica">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 80 80" role="img" aria-label="Multica">
   <polygon
     fill="#111827"
-    points="25,51.1 25,80 35,80 35,51.1 61.8,77.9 68.9,70.8 42.1,44 80,44 80,34 42.1,34 68.9,7.2 61.8,0.1 35,26.9 35,-11 25,-11 25,26.9 -1.8,0.1 -8.9,7.2 17.9,34 -20,34 -20,44 17.9,44 -8.9,70.8 -1.8,77.9"
-    transform="translate(30, 20) scale(0.75)"
+    points="35,51.1 35,80 45,80 45,51.1 71.8,77.9 78.9,70.8 52.1,44 90,44 90,34 52.1,34 78.9,7.2 71.8,0.1 45,26.9 45,-11 35,-11 35,26.9 8.2,0.1 1.1,7.2 27.9,34 -10,34 -10,44 27.9,44 1.1,70.8 8.2,77.9"
+    transform="translate(5, 5.5) scale(0.87)"
   />
-  <text x="95" y="62" font-family="-apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif" font-size="48" font-weight="700" fill="#111827" letter-spacing="-1">Multica</text>
 </svg>