feat(projects): add createProject service (manual, shared numbering)

Introduces CreateProjectSchema (Zod 4, NaN-guarded coercions), the
createProject() service function (atomic shared-number generation inside
a $transaction), getNextProjectNumber() preview helper, and two Vitest
tests that verify standalone project creation and distinct sequential
numbers. Routes are deferred to a subsequent task.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/projects.service.ts

@@ -1,6 +1,11 @@
 import prisma from "../config/database";
-import { releaseSharedNumber } from "./numbering.service";
+import {
+  generateSharedNumber,
+  previewSharedNumber,
+  releaseSharedNumber,
+} from "./numbering.service";
 import { NasFileManager } from "./nas-file-manager";
+import type { CreateProjectInput } from "../schemas/projects.schema";
 
 const nasFileManager = new NasFileManager();
 
@@ -144,6 +149,60 @@ export async function updateProject(id: number, body: Record<string, any>) {
   return updated;
 }
 
+/**
+ * Create a standalone (manual) project. Takes the next SHARED number — the
+ * same pool orders/projects draw from — generated atomically inside the
+ * transaction (SELECT … FOR UPDATE via getNextSequence). order_id stays null,
+ * which is what marks it "samostatný" in the UI. NAS folder creation is
+ * best-effort (the manager self-guards isConfigured() and swallows fs errors).
+ */
+export async function createProject(data: CreateProjectInput) {
+  if (data.customer_id != null) {
+    const customer = await prisma.customers.findUnique({
+      where: { id: data.customer_id },
+    });
+    if (!customer) return { error: "Zákazník nenalezen", status: 400 };
+  }
+  if (data.responsible_user_id != null) {
+    const user = await prisma.users.findUnique({
+      where: { id: data.responsible_user_id },
+    });
+    if (!user) return { error: "Zodpovědná osoba nenalezena", status: 400 };
+  }
+
+  const project = await prisma.$transaction(async (tx) => {
+    const project_number = await generateSharedNumber(tx);
+    return tx.projects.create({
+      data: {
+        project_number,
+        name: data.name,
+        customer_id: data.customer_id ?? null,
+        responsible_user_id: data.responsible_user_id ?? null,
+        status: data.status || "aktivni",
+        start_date: data.start_date ? new Date(data.start_date) : null,
+        end_date: data.end_date ? new Date(data.end_date) : null,
+        notes: data.notes ?? null,
+        order_id: null,
+        quotation_id: null,
+      },
+    });
+  });
+
+  if (project.project_number && nasFileManager.isConfigured()) {
+    nasFileManager.createProjectFolder(
+      project.project_number,
+      project.name || "",
+    );
+  }
+
+  return project;
+}
+
+/** Preview the next shared number for the create form (does NOT consume it). */
+export async function getNextProjectNumber(): Promise<string> {
+  return previewSharedNumber();
+}
+
 export async function deleteProject(id: number, deleteFiles: boolean = false) {
   const existing = await prisma.projects.findUnique({ where: { id } });
   if (!existing) return { error: "not_found" as const };