fix: prevent WebKit/GTK system theme from overriding input text colors on Linux

On Linux, WebKit inherits GTK system text colors for form controls,
causing dark-on-dark text in dark mode. Explicitly set color and
-webkit-text-fill-color on inputs/textareas/buttons, and add
color-scheme: dark to .dark so WebKit uses the correct system UI
color scheme.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

src/styles/globals.css

@@ -51,4 +51,21 @@
 @layer base {
   * { @apply border-border; }
   body { @apply bg-background text-foreground; }
+
+  /* Prevent WebKit/GTK from overriding form control colors with system theme */
+  input, textarea, select, button {
+    color: hsl(var(--foreground));
+    background-color: hsl(var(--background));
+    -webkit-text-fill-color: hsl(var(--foreground));
+  }
+
+  input::placeholder, textarea::placeholder {
+    color: hsl(var(--muted-foreground));
+    -webkit-text-fill-color: hsl(var(--muted-foreground));
+    opacity: 1;
+  }
 }
+
+/* Tell WebKit which color scheme is active so system UI elements match */
+:root { color-scheme: light; }
+.dark { color-scheme: dark; }