feat: slide panels, task calendar, team management, project editing, collapsible sections

- Add SlidePanel, TaskDetailPanel, PostDetailPanel, TeamPanel, TeamMemberPanel
- Add ProjectEditPanel, CollapsibleSection, DatePresetPicker, TaskCalendarView
- Update App, AuthContext, i18n (ar/en), PostProduction, ProjectDetail, Projects
- Update Settings, Tasks, Team pages
- Update InteractiveTimeline, MemberCard, ProjectCard, TaskCard components
- Update server API utilities
- Remove tracked server/node_modules (now properly gitignored)

client/src/components/CollapsibleSection.jsx

@@ -0,0 +1,20 @@
+import { useState } from 'react'
+import { ChevronDown, ChevronRight } from 'lucide-react'
+
+export default function CollapsibleSection({ title, defaultOpen = true, badge, children, noBorder }) {
+  const [open, setOpen] = useState(defaultOpen)
+
+  return (
+    <div className={noBorder ? '' : 'border-b border-border'}>
+      <button
+        onClick={() => setOpen(!open)}
+        className="w-full flex items-center gap-2 px-5 py-3 text-sm font-semibold text-text-primary hover:bg-surface-secondary transition-colors"
+      >
+        {open ? <ChevronDown className="w-4 h-4" /> : <ChevronRight className="w-4 h-4" />}
+        {title}
+        {badge}
+      </button>
+      {open && children}
+    </div>
+  )
+}