feat: add workspace management features including member invitations and role updates

- Implemented API endpoints for managing workspace members (GET, POST, PATCH, DELETE).
- Added workspace creation and retrieval functionalities.
- Enhanced project model to associate with workspaces.
- Updated project member roles and access control logic.
- Created sign-out page and updated authentication flow.
- Modified header to include navigation to workspaces.
- Updated Prisma schema to include workspace and member models.
- Seed script updated to create demo workspaces and associated members.

app/api/workspaces/route.ts

@@ -0,0 +1,96 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+import { auth } from '@/lib/auth';
+
+// GET /api/workspaces - List all workspaces for the authenticated user
+export async function GET() {
+    try {
+        const session = await auth();
+
+        if (!session?.user?.id) {
+            return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+        }
+
+        // Get workspaces where user is owner OR a member
+        const workspaces = await db.workspace.findMany({
+            where: {
+                OR: [
+                    { ownerId: session.user.id },
+                    { members: { some: { userId: session.user.id } } },
+                ],
+            },
+            include: {
+                owner: { select: { id: true, name: true, image: true } },
+                _count: { select: { projects: true, members: true } },
+            },
+            orderBy: { updatedAt: 'desc' },
+        });
+
+        return NextResponse.json({ workspaces });
+    } catch (error) {
+        console.error('Error fetching workspaces:', error);
+        return NextResponse.json(
+            { error: 'Failed to fetch workspaces' },
+            { status: 500 }
+        );
+    }
+}
+
+// POST /api/workspaces - Create a new workspace
+export async function POST(request: NextRequest) {
+    try {
+        const session = await auth();
+
+        if (!session?.user?.id) {
+            return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+        }
+
+        const body = await request.json();
+        const { name, description } = body;
+
+        if (!name || typeof name !== 'string' || name.trim().length === 0) {
+            return NextResponse.json(
+                { error: 'Workspace name is required' },
+                { status: 400 }
+            );
+        }
+
+        // Generate slug
+        const baseSlug = name
+            .toLowerCase()
+            .trim()
+            .replace(/[^a-z0-9\s-]/g, '')
+            .replace(/\s+/g, '-')
+            .replace(/-+/g, '-');
+
+        let slug = baseSlug;
+        let attempts = 0;
+        while (attempts < 10) {
+            const existing = await db.workspace.findUnique({ where: { slug } });
+            if (!existing) break;
+            slug = `${baseSlug}-${Math.random().toString(36).substring(2, 6)}`;
+            attempts++;
+        }
+
+        const workspace = await db.workspace.create({
+            data: {
+                name: name.trim(),
+                description: description?.trim() || null,
+                slug,
+                ownerId: session.user.id,
+            },
+            include: {
+                owner: { select: { id: true, name: true, image: true } },
+                _count: { select: { projects: true, members: true } },
+            },
+        });
+
+        return NextResponse.json(workspace, { status: 201 });
+    } catch (error) {
+        console.error('Error creating workspace:', error);
+        return NextResponse.json(
+            { error: 'Failed to create workspace' },
+            { status: 500 }
+        );
+    }
+}