feat(*): svelte 5 panel view sharing the gateway ui, obsidian theme, preview and tests

src/state.svelte.ts

@@ -0,0 +1,8 @@
+// What a panel leaf remembers: the conversation on screen, whether it follows
+// the active note, and which note that is. Reactive so the view and the
+// Svelte tree share one truth.
+export class PanelState {
+  selected = $state<string | null>(null);
+  follow = $state(true);
+  sourcePath = $state("");
+}