journal: real markdown editor (EasyMDE) with live preview toggle, fix default template

- Replace the plain textarea with EasyMDE (vendored locally, no CDN) for
  markdown authoring: syntax highlighting, smart list continuation, and a
  custom text-based toolbar (built-in EasyMDE toolbar icons require Font
  Awesome from a CDN, which this app doesn't use). unorderedListStyle is set
  to "-" to match the app's own template convention.
- Add a preview/edit toggle button that swaps the editor for the exact same
  server-rendered markdown (via /journal/preview) shown after saving, instead
  of always showing both.
- Fix create/edit entry routes to verify the submitted category_id actually
  belongs to the current user before inserting -- every other write path in
  this app already checked ownership; this one didn't (found while manually
  testing the new editor with a typo'd category id that happened to belong to
  someone else's category, which surfaced as an IntegrityError 500 instead of
  a clean 404-equivalent).
- Fix the default "일상" category template: bare "-" bullet lines don't parse
  as list items in the markdown renderer (they need a trailing space), and
  the content_template validator was silently stripping that trailing space
  off on every save. Backfill migration updates any category still holding
  the old, broken template text.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/static/js/journal-editor.js

@@ -0,0 +1,45 @@
+(function () {
+  // 내장 툴바(toolbar: false)는 안 쓴다 — EasyMDE 기본 툴바 아이콘은 Font Awesome CDN을 전제로
+  // 하는데, 이 앱은 CDN을 안 쓰는 게 원칙이라 대신 journal.html/journal_day_detail.html에서
+  // 직접 만든 텍스트 버튼이 아래 EDITOR_ACTIONS로 EasyMDE 인스턴스 메서드를 호출한다.
+  function initEditors(root) {
+    if (typeof EasyMDE === "undefined") return;
+    var scope = root instanceof Element ? root : document;
+    var textareas = scope.querySelectorAll("textarea.markdown-editor:not([data-easymde-initialized])");
+
+    textareas.forEach(function (textarea) {
+      textarea.setAttribute("data-easymde-initialized", "true");
+
+      var easymde = new EasyMDE({
+        element: textarea,
+        toolbar: false,
+        spellChecker: false,
+        autoDownloadFontAwesome: false,
+        status: false,
+        placeholder: textarea.getAttribute("placeholder") || "",
+        minHeight: (textarea.getAttribute("rows") || 6) * 24 + "px",
+        // 글머리 목록 버튼/Enter 자동 이어쓰기가 기본 "*" 대신 "-"를 쓰게 한다.
+        // 서버 렌더링(app/markdown_utils.py)은 -/*/+ 전부 동일하게 처리하니 렌더링과는 무관하고
+        // 순수하게 에디터가 새로 만들어주는 글머리 기호에 대한 취향 설정이다.
+        unorderedListStyle: "-",
+      });
+
+      // CodeMirror는 원본 textarea와 실시간으로 값이 동기화되지 않는다(.save()를 명시적으로
+      // 불러야 함) — 매 변경마다 저장하고, htmx 미리보기(hx-trigger="input ...")와
+      // Alpine x-model이 둘 다 반응하도록 input 이벤트를 합성해서 던진다.
+      easymde.codemirror.on("change", function () {
+        easymde.codemirror.save();
+        textarea.dispatchEvent(new Event("input", { bubbles: true }));
+      });
+
+      textarea._easymde = easymde;
+    });
+  }
+
+  document.addEventListener("DOMContentLoaded", function () {
+    initEditors(document);
+  });
+  document.body.addEventListener("htmx:afterSwap", function (evt) {
+    initEditors(evt.target);
+  });
+})();