chore: move FX rates page to /fx-rates, remove old snippet, add OG image

Move sample-rates.mdx from platform-overview/core-concepts/ to top-level
fx-rates.mdx for a cleaner URL path. Delete the superseded rate-explorer
snippet and add a dedicated OG image for the FX Rates page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: patcapulong

mintlify/docs.json

@@ -56,7 +56,7 @@
               "platform-overview/core-concepts/account-model",
               "platform-overview/core-concepts/transaction-lifecycle",
               "platform-overview/core-concepts/currencies-and-rails",
-              "platform-overview/core-concepts/sample-rates",
+              "fx-rates",
               "platform-overview/configuration"
             ]
           }

…-overview/core-concepts/sample-rates.mdx mintlify/fx-rates.mdxmintlify/platform-overview/core-concepts/sample-rates.mdx renamed to mintlify/fx-rates.mdx mintlify/platform-overview/core-concepts/sample-rates.mdx renamed to mintlify/fx-rates.mdx

@@ -2,7 +2,7 @@
 title: "FX Rates"
 description: "Compare Grid's FX rates against major providers across 40+ corridors"
 icon: "/images/icons/globe.svg"
-"og:image": "/images/og/og-get-started.png"
+"og:image": "/images/og/og-fx-rates.png"
 mode: "wide"
 ---