Replace all:unset with explicit button/input resets across Foundry UI

Styletron's generated stylesheet ordering makes all:unset unreliable —
it can override font-size, border-radius, and background unpredictably.
Replace with appearance:none + targeted resets and clean up duplicate
CSS properties introduced during iterative fixes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

factory/packages/frontend/src/components/mock-layout/model-picker.tsx

@@ -138,7 +138,10 @@ export const ModelPicker = memo(function ModelPicker({
       <div className={css({ display: "inline-flex" })}>
         <button
           className={css({
-            all: "unset",
+            appearance: "none",
+            WebkitAppearance: "none",
+            background: "none",
+            margin: "0",
             display: "flex",
             alignItems: "center",
             gap: "4px",