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/pages/Projects.jsx

@@ -143,6 +143,7 @@ export default function Projects() {
             status: project.status,
             priority: project.priority,
             assigneeName: project.ownerName || project.owner_name,
+            thumbnailUrl: project.thumbnail_url || project.thumbnailUrl,
             tags: [project.status, project.priority].filter(Boolean),
           })}
           onDateChange={async (projectId, { startDate, endDate }) => {