Update application UI with a modern and streamlined design

Revamp the entire UI with a new theme, enhancing readability and modern aesthetics across all components, including AI chat, calendar, media uploads, and user management sections.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ae4037a0-2a6f-4530-9bac-79b543286bda
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/397bca8c-984f-43ff-841a-10897aeb8140/ae4037a0-2a6f-4530-9bac-79b543286bda/nriKMjY

client/src/pages/calendar.tsx

@@ -25,8 +25,8 @@ export default function Calendar() {
       <main className="flex-1 overflow-y-auto">
         <TopBar onMenuClick={() => setSidebarOpen(!sidebarOpen)} />
         
-        <div className="p-6">
-          <div className="mb-6">
+        <div className="p-8 max-w-[1600px] mx-auto">
+          <div className="mb-8">
             <h1 className="text-3xl font-bold text-foreground">Calendrier</h1>
             <p className="text-muted-foreground mt-2">
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