refactor(dev): dogfood framework CSS in theme adapter panel

Replace all inline styles in theme-adapter.js with framework classes.
The panel now uses its own tokens (var(--bg-1), var(--fg-0), etc.) so
it visually adapts when you change theme colors — true dogfooding.

New framework components added to fill gaps:
- popover.css — fixed-position floating panel (.popover, .popover-br)
- chip.css + chip.cljc — selectable preset buttons (.chip, .chip-active)
- swatch.css — color preview strips (.swatch-row, .swatch)
- button.css — icon-only buttons (.btn-icon, .btn-icon-round)
- card.css — sectioned card variant (.card-flush, .card-section)
- utilities.css — text/flex helpers (.text-xs, .font-semibold, .flex-1, etc.)

Theme adapter JS shrunk from 340 to 250 lines by removing the 60-line
inline style object and applyStyle() helper.

src/ui/popover.css

@@ -0,0 +1,12 @@
+/* ── Popover ────────────────────────────────────────────────────── */
+/* Fixed-position floating panel. Combine with a corner class.     */
+
+.popover {
+  position: fixed;
+  z-index: 9999;
+}
+
+.popover-br { bottom: var(--size-4); right: var(--size-4); }
+.popover-bl { bottom: var(--size-4); left: var(--size-4); }
+.popover-tr { top: var(--size-4); right: var(--size-4); }
+.popover-tl { top: var(--size-4); left: var(--size-4); }