feat(editor): paste and drop images into Markdown files (#489)

Pasting or dropping an image into a Markdown editor saves it beside the document in `assets/` and inserts a URL-encoded relative link as one undo step, in local and remote projects. Existing names get numbered suffixes; the folder and clipboard name pattern are in Settings › Editor › General. Non-Markdown editors, text paste and other dropped files keep their behavior.

Fixes #308

src/features/settings/pages/editor/general.tsx

@@ -95,6 +95,23 @@ const GENERAL = editorPage({
   projectScope: true,
   keywords: ["mouse", "scroll", "wrap", "trailing spaces", "save"],
   sections: [
+    {
+      title: "Markdown Images",
+      items: [
+        {
+          t: "text",
+          key: `${P}.general.markdownImageFolder`,
+          label: "Image folder",
+          hint: "Relative to the Markdown file.",
+        },
+        {
+          t: "text",
+          key: `${P}.general.markdownImageNamePattern`,
+          label: "Image name pattern",
+          hint: "For clipboard images: {timestamp} becomes YYYYMMDD-HHmmss. Source file names are preserved.",
+        },
+      ],
+    },
     {
       title: "Mouse Control",
       items: [