docs: add clarification for assets/static

docs/latest/concepts/static-files.md

@@ -16,6 +16,32 @@ const app = new App()
   .use(staticFiles());
 ```
 
+## Imported assets vs static files
+
+When using Fresh with Vite (now the default), **files that you import in your
+JavaScript/TypeScript code should not be placed in the `static/` folder**. This
+prevents file duplication during the build process.
+
+```tsx client.ts
+// ❌ Don't import from static/
+import "./static/styles.css";
+
+// ✅ Import from outside static/ (e.g., assets/)
+import "./assets/styles.css";
+```
+
+**Rule of thumb:**
+
+- Files **imported in code** (CSS, icons, etc.) → Place outside `static/` (e.g.,
+  in an `assets/` folder)
+- Files **referenced by URL path** (favicon.ico, fonts, robots.txt, PDFs, etc.)
+  → Place in `static/`
+
+When you import a file in your code, Vite processes it through its build
+pipeline, optimizes it, and adds a content hash to the filename for cache
+busting. Keeping these files outside `static/` ensures they're only included
+once in your build output.
+
 ## Caching headers
 
 By default, Fresh adds caching headers for the `src` and `srcset` attributes on