feat: add complex user invitation and management features

- Implemented complex member and invitation schemas using Zod for validation.
- Created new API endpoints for inviting, accepting, revoking, and canceling complex user invitations.
- Developed handlers for managing complex users, including listing, inviting, revoking, and canceling invitations.
- Added frontend components for displaying and managing complex users and invitations.
- Introduced session storage management for pending invitations.
- Integrated Gravatar for user avatars based on email.
- Created database migration for complex invitations table.

apps/backend/prisma/migrations/20260422120000_add_complex_invitations/migration.sql

@@ -0,0 +1,26 @@
+-- CreateTable
+CREATE TABLE "complex_invitations" (
+    "id" UUID NOT NULL,
+    "complex_id" UUID NOT NULL,
+    "email" VARCHAR(255) NOT NULL,
+    "token_hash" TEXT NOT NULL,
+    "expires_at" TIMESTAMP(3) NOT NULL,
+    "accepted_at" TIMESTAMP(3),
+    "revoked_at" TIMESTAMP(3),
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updated_at" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "complex_invitations_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "complex_invitations_token_hash_key" ON "complex_invitations"("token_hash");
+
+-- CreateIndex
+CREATE INDEX "complex_invitations_complex_id_email_idx" ON "complex_invitations"("complex_id", "email");
+
+-- CreateIndex
+CREATE INDEX "complex_invitations_email_idx" ON "complex_invitations"("email");
+
+-- AddForeignKey
+ALTER TABLE "complex_invitations" ADD CONSTRAINT "complex_invitations_complex_id_fkey" FOREIGN KEY ("complex_id") REFERENCES "complexes"("id") ON DELETE CASCADE ON UPDATE CASCADE;