feat(env): Update environment configuration and enhance email functionality

- Renamed DATABASE_URL to POSTGRES_URL in .env.example for clarity.
- Added SMTP configuration for email sending, including host, port, user, password, and from address.
- Updated package.json to include new dependencies for email handling and UI components.
- Modified middleware to handle public and protected routes more effectively.
- Enhanced API routes for studies to support user roles and permissions.
- Updated database schema to include invitations and user roles related to studies.
- Improved user permissions handling in the permissions module.
- Added new utility functions for managing user roles and study access.

src/app/api/invitations/accept/[token]/route.ts

@@ -0,0 +1,64 @@
+import { eq, and, gt } from "drizzle-orm";
+import { NextResponse } from "next/server";
+import { auth } from "@clerk/nextjs/server";
+import { db } from "~/db";
+import { invitationsTable, userRolesTable } from "~/db/schema";
+
+export async function POST(
+  request: Request,
+  { params }: { params: { token: string } }
+) {
+  const { userId } = await auth();
+  
+  if (!userId) {
+    return new NextResponse("Unauthorized", { status: 401 });
+  }
+
+  try {
+    const { token } = params;
+
+    // Find the invitation
+    const [invitation] = await db
+      .select()
+      .from(invitationsTable)
+      .where(
+        and(
+          eq(invitationsTable.token, token),
+          eq(invitationsTable.accepted, false),
+          gt(invitationsTable.expiresAt, new Date())
+        )
+      )
+      .limit(1);
+
+    if (!invitation) {
+      return new NextResponse(
+        "Invitation not found or has expired",
+        { status: 404 }
+      );
+    }
+
+    // Start a transaction
+    await db.transaction(async (tx) => {
+      // Mark invitation as accepted
+      await tx
+        .update(invitationsTable)
+        .set({ accepted: true })
+        .where(eq(invitationsTable.id, invitation.id));
+
+      // Assign role to user for this specific study
+      await tx
+        .insert(userRolesTable)
+        .values({
+          userId,
+          roleId: invitation.roleId,
+          studyId: invitation.studyId,
+        })
+        .onConflictDoNothing();
+    });
+
+    return new NextResponse("Invitation accepted", { status: 200 });
+  } catch (error) {
+    console.error("Error accepting invitation:", error);
+    return new NextResponse("Internal Server Error", { status: 500 });
+  }
+}