fix: set dialog text color to use theme foreground

The native `<dialog>` element has browser-default black text that
doesn't inherit from the body, making it unreadable in dark mode.

src/ui/dialog.css

@@ -7,6 +7,7 @@
   margin: auto;
   padding: 0;
   background: var(--bg-1);
+  color: var(--fg-0);
   border: var(--border-0);
   border-radius: var(--radius-lg);
   box-shadow: var(--shadow-3);