appview/strings: replace leftover references to "gist"s

Signed-off-by: ItsHarper <[e-mail]>

appview/pages/templates/strings/string.html

···
             title="Delete string"
             hx-delete="/strings/{{ .String.Did }}/{{ .String.Rkey }}/"
             hx-swap="none"
-            hx-confirm="Are you sure you want to delete the gist `{{ .String.Filename }}`?"
+            hx-confirm="Are you sure you want to delete the string `{{ .String.Filename }}`?"
           >
             {{ i "trash-2" "size-4" }}
             <span class="hidden md:inline">delete</span> 

appview/strings/strings.go

···
 	}
 
 	if user.Did != id.DID.String() {
-		fail("You cannot delete this gist", fmt.Errorf("unauthorized deletion, %s != %s", user.Did, id.DID.String()))
+		fail("You cannot delete this string", fmt.Errorf("unauthorized deletion, %s != %s", user.Did, id.DID.String()))
 		return
 	}