Initial commit: design-018 Phases 0-5 (stomping.me)

Auth BFF (OIDC + prompt=none silent SSO), Mongo data layer, admin CRUD
(folders/tags/stories/chapters with TipTap), public reader with tag
filtering. Built and verified same-session per design-018-stories.md.

src/lib/storyAggregate.js

@@ -0,0 +1,21 @@
+// storyAggregate.js — story.word_count is the sum of its published chapters'
+// word counts (design-018 §2.2). Recomputed on every chapter save/publish-
+// toggle/delete — full recount each time, matching this project's established
+// "cheap at this scale, full recount is correct" convention (design-018 §2.6
+// documents the same tradeoff for rating aggregates).
+'use strict';
+
+async function recomputeStoryWordCount(db, storyId) {
+  const chapters = await db.collection('chapters')
+    .find({ story_id: storyId, status: 'published' }, { projection: { word_count: 1 } })
+    .toArray();
+  const wordCount = chapters.reduce((sum, c) => sum + (c.word_count || 0), 0);
+
+  await db.collection('stories').updateOne(
+    { _id: storyId },
+    { $set: { word_count: wordCount, updated_at: new Date() } }
+  );
+  return wordCount;
+}
+
+module.exports = { recomputeStoryWordCount };