feat: implement Story 1.1 — create and view diagrams

Add diagram/project DB schema, CRUD API, dashboard pages with grid/card/
empty state, create dialog with type selector, editor placeholder, and
26 schema validation tests. Includes code review fixes: soft-delete
filter on GET /:id, error handling, keyboard accessibility, type-safe
API response types, and error states on pages.

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

packages/api/tests/diagram/diagram-db-schema.test.ts

@@ -0,0 +1,112 @@
+import { describe, it, expect } from "vitest";
+
+import {
+  insertDiagramSchema,
+  selectDiagramSchema,
+  insertProjectSchema,
+  selectProjectSchema,
+} from "@turbostarter/db/schema";
+
+describe("insertDiagramSchema", () => {
+  it("should accept valid diagram insert data", () => {
+    const result = insertDiagramSchema.safeParse({
+      title: "Test Diagram",
+      type: "flowchart",
+      userId: "user-123",
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it("should reject missing required fields", () => {
+    const result = insertDiagramSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+
+  it("should reject invalid diagram type", () => {
+    const result = insertDiagramSchema.safeParse({
+      title: "Test",
+      type: "invalid-type",
+      userId: "user-123",
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it("should accept all valid diagram types", () => {
+    const types = ["bpmn", "er", "orgchart", "architecture", "sequence", "flowchart"];
+    for (const type of types) {
+      const result = insertDiagramSchema.safeParse({
+        title: "Test",
+        type,
+        userId: "user-123",
+      });
+      expect(result.success).toBe(true);
+    }
+  });
+
+  it("should accept optional fields", () => {
+    const result = insertDiagramSchema.safeParse({
+      title: "Test",
+      type: "bpmn",
+      userId: "user-123",
+      projectId: "proj-123",
+      lastAiMessage: "Hello",
+      graphData: { nodes: [] },
+    });
+    expect(result.success).toBe(true);
+  });
+});
+
+describe("selectDiagramSchema", () => {
+  it("should accept a complete diagram record", () => {
+    const result = selectDiagramSchema.safeParse({
+      id: "diag-123",
+      title: "Test Diagram",
+      type: "er",
+      graphData: {},
+      userId: "user-123",
+      projectId: null,
+      lastAiMessage: null,
+      deletedAt: null,
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    });
+    expect(result.success).toBe(true);
+  });
+});
+
+describe("insertProjectSchema", () => {
+  it("should accept valid project insert data with field assertions", () => {
+    const result = insertProjectSchema.safeParse({
+      name: "My Project",
+      userId: "user-123",
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.name).toBe("My Project");
+      expect(result.data.userId).toBe("user-123");
+    }
+  });
+
+  it("should accept optional sortOrder", () => {
+    const result = insertProjectSchema.safeParse({
+      name: "My Project",
+      userId: "user-123",
+      sortOrder: 5,
+    });
+    expect(result.success).toBe(true);
+  });
+});
+
+describe("selectProjectSchema", () => {
+  it("should accept a complete project record", () => {
+    const result = selectProjectSchema.safeParse({
+      id: "proj-123",
+      name: "My Project",
+      userId: "user-123",
+      sortOrder: 0,
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    });
+    expect(result.success).toBe(true);
+  });
+});