perf(pages): stream asset files instead of buffering in memory

Replace full-file buffering with io.Copy streaming in serveRepoFileAsset. Reduces memory usage for large assets (images, videos) by streaming directly from git blob to HTTP response. Adds Content-Length header for better client handling.

routers/web/pages/pages.go

@@ -843,15 +843,9 @@ func serveRepoFileAsset(ctx *context.Context, commit *git.Commit, assetPath stri
 	ctx.Resp.Header().Set("Content-Type", contentType)
 	ctx.Resp.Header().Set("Cache-Control", "public, max-age=3600")
 
-	// Stream content
-	content := make([]byte, entry.Blob().Size())
-	_, err = reader.Read(content)
-	if err != nil && err.Error() != "EOF" {
-		ctx.ServerError("Failed to read asset", err)
-		return
-	}
-
-	_, _ = ctx.Resp.Write(content)
+	// Stream content directly to the response
+	ctx.Resp.Header().Set("Content-Length", strconv.FormatInt(entry.Blob().Size(), 10))
+	_, _ = io.Copy(ctx.Resp, reader)
 }
 
 // servePageEvent handles POST /pages/events for A/B test event tracking