fix: preset thumbnails no longer conflict with main preview animation

- Inject only @keyframes (not .animated class rule) per preset thumbnail
  so the main preview's .animated rule cannot override them
- Drive thumbnail animation entirely via inline style properties
- Remove isActive/currentName — presets should never appear selected

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

lib/animate/cssBuilder.ts

@@ -61,6 +61,24 @@ export function buildAnimationShorthand(config: AnimationConfig): string {
   return `${config.name} ${config.duration}ms ${config.easing}${delay} ${iter} ${config.direction} ${config.fillMode}`;
 }
 
+export function buildKeyframesOnly(config: AnimationConfig): string {
+  const sorted = [...config.keyframes].sort((a, b) => a.offset - b.offset);
+  let out = `@keyframes ${config.name} {\n`;
+  for (const kf of sorted) {
+    const lines = buildProperties(kf.properties);
+    if (lines.length === 0) {
+      out += `  ${kf.offset}% { }\n`;
+    } else {
+      out += `  ${kf.offset}% {\n`;
+      for (const line of lines) out += `    ${line};\n`;
+      if (kf.easing) out += `    animation-timing-function: ${kf.easing};\n`;
+      out += `  }\n`;
+    }
+  }
+  out += `}\n`;
+  return out;
+}
+
 export function buildCSS(config: AnimationConfig): string {
   const sorted = [...config.keyframes].sort((a, b) => a.offset - b.offset);