fix(frontend): load sweep-shared.css once from main.ts — a shared <style src> breaks vite build (#3207)

plugin-vue throws "Cannot read properties of undefined (reading 'scoped')"
when several SFCs share one src stylesheet. vue-tsc passed, so only the
image job caught it; :dev has not rebuilt since 22b7a92.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/main.ts

@@ -6,6 +6,9 @@ import "./assets/theme.css";
 // After theme.css — it consumes the tokens declared there.
 import "./assets/components.css";
 import "./assets/prose.css";
+// Global rather than `<style src>` per pane: plugin-vue cannot compile one
+// src stylesheet shared by several SFCs (#3207 broke the image build).
+import "./assets/sweep-shared.css";
 
 const app = createApp(App);
 app.use(createPinia());