fix: keep the line breaks an author typed

Text written across several lines rendered as one run-on line. Markdown reads a
single newline as a space that joins a paragraph, the parser leaves that
newline inside the text node, and HTML then collapses it — so the break the
author pressed Enter for disappeared at the last step.

This was never a preview artifact: the Studio preview and the public page go
through the same renderer, so a published record ran its lines together too.

Newlines inside a paragraph now render as <br>. Paragraphs separated by a blank
line are already two paragraphs by the time they reach here, so this only
affects the breaks an author put inside one.

tests/component/inline-line-breaks.test.tsx

@@ -0,0 +1,36 @@
+// @vitest-environment jsdom
+
+import { render } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+
+import { InlineRenderer } from "../../src/features/tech-log/presentation/shared/public-render/inline-renderer.tsx";
+
+/**
+ * 작성자가 엔터로 나눠 쓴 글이 한 줄로 이어져 보였다. Markdown 이 한 번의 줄바꿈을 문단 내 공백으로
+ * 읽고, 파서가 그 줄바꿈을 텍스트에 남긴 뒤, HTML 이 다시 공백으로 접기 때문이다. 미리보기와 공개
+ * 화면이 같은 렌더러를 쓰므로 두 곳 모두에서 그랬다.
+ */
+describe("문단 안의 줄바꿈", () => {
+  it("줄바꿈을 <br> 로 그린다", () => {
+    const { container } = render(
+      <InlineRenderer content={[{ type: "TEXT", text: "첫째 줄\n둘째 줄" }]} />,
+    );
+    expect(container.querySelectorAll("br")).toHaveLength(1);
+    expect(container.textContent).toBe("첫째 줄둘째 줄");
+  });
+
+  it("줄바꿈이 없으면 <br> 를 넣지 않는다", () => {
+    const { container } = render(
+      <InlineRenderer content={[{ type: "TEXT", text: "한 줄" }]} />,
+    );
+    expect(container.querySelectorAll("br")).toHaveLength(0);
+    expect(container.textContent).toBe("한 줄");
+  });
+
+  it("여러 번 엔터를 친 만큼 내려간다", () => {
+    const { container } = render(
+      <InlineRenderer content={[{ type: "TEXT", text: "가\n나\n다" }]} />,
+    );
+    expect(container.querySelectorAll("br")).toHaveLength(2);
+  });
+});