refactor: complete docs logo PNG-to-SVG migration (#1601)

Update docs.json logo paths from PNG to SVG, matching the frontend
convention (sencho-logo-dark.svg / sencho-logo-light.svg). Remove old
PNG assets from docs/images/logo/.

docs/docs.json

@@ -8,8 +8,8 @@
     "dark": "#00BEC7"
   },
   "logo": {
-    "light": "/images/logo/logo-light.png",
-    "dark": "/images/logo/logo-dark.png",
+    "light": "/images/logo/sencho-logo-light.svg",
+    "dark": "/images/logo/sencho-logo-dark.svg",
     "href": "https://sencho.io"
   },
   "favicon": "/images/logo/favicon.ico",