ui: persist issue properties pane visibility in localStorage

Store the open/closed state of the properties panel in localStorage
so it persists across navigations, issues, and companies.

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

ui/src/context/PanelContext.tsx

@@ -1,15 +1,38 @@
 import { createContext, useCallback, useContext, useState, type ReactNode } from "react";
 
+const STORAGE_KEY = "paperclip:panel-visible";
+
 interface PanelContextValue {
   panelContent: ReactNode | null;
+  panelVisible: boolean;
   openPanel: (content: ReactNode) => void;
   closePanel: () => void;
+  setPanelVisible: (visible: boolean) => void;
+  togglePanelVisible: () => void;
 }
 
 const PanelContext = createContext<PanelContextValue | null>(null);
 
+function readPreference(): boolean {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    return raw === null ? true : raw === "true";
+  } catch {
+    return true;
+  }
+}
+
+function writePreference(visible: boolean) {
+  try {
+    localStorage.setItem(STORAGE_KEY, String(visible));
+  } catch {
+    // Ignore storage failures.
+  }
+}
+
 export function PanelProvider({ children }: { children: ReactNode }) {
   const [panelContent, setPanelContent] = useState<ReactNode | null>(null);
+  const [panelVisible, setPanelVisibleState] = useState(readPreference);
 
   const openPanel = useCallback((content: ReactNode) => {
     setPanelContent(content);
@@ -19,8 +42,23 @@ export function PanelProvider({ children }: { children: ReactNode }) {
     setPanelContent(null);
   }, []);
 
+  const setPanelVisible = useCallback((visible: boolean) => {
+    setPanelVisibleState(visible);
+    writePreference(visible);
+  }, []);
+
+  const togglePanelVisible = useCallback(() => {
+    setPanelVisibleState((prev) => {
+      const next = !prev;
+      writePreference(next);
+      return next;
+    });
+  }, []);
+
   return (
-    <PanelContext.Provider value={{ panelContent, openPanel, closePanel }}>
+    <PanelContext.Provider
+      value={{ panelContent, panelVisible, openPanel, closePanel, setPanelVisible, togglePanelVisible }}
+    >
       {children}
     </PanelContext.Provider>
   );