Externalize @codemirror/state and @codemirror/view from the bundle

Obsidian ships CodeMirror in its runtime; bundling our own copy is
both wasteful (~200 kB) and risky (two CM6 instances in the host).
The bundling-by-default also broke pnpm installs because pnpm doesn't
hoist devDependencies the way npm does, so Rollup couldn't resolve
the import paths.

Externalising drops the plugin back to ~620 kB and matches the
recommended pattern for Obsidian plugins that use CM6.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

vite.config.ts

@@ -34,7 +34,14 @@ export default defineConfig({
       fileName: () => "main.js",
     },
     rollupOptions: {
-      external: ["obsidian", "electron"], // don't bundle the host libs
+      // Obsidian's runtime already loads CodeMirror; importing it as a peer
+      // keeps our bundle small and avoids two CM6 instances in the host.
+      external: [
+        "obsidian",
+        "electron",
+        "@codemirror/state",
+        "@codemirror/view",
+      ],
       output: {
         exports: "named",
         assetFileNames: () => "styles.css", // Always output CSS as styles.css