feat: add show/hide read items and fix individual mark-read

- Add countReadItems function to storage/items.js
- Update getTimelineItems to filter out read items by default
- Add showRead query param support to channel controller
- Update channel.njk with show/hide read toggle buttons
- Add "All caught up!" state when all items are read
- Add JavaScript handler for individual mark-read buttons
- Mark-read now hides the item with smooth animation
- Add locale strings: showRead, hideRead, allRead

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/storage/items.js

@@ -78,6 +78,7 @@ export async function addItem(application, { channelId, feedId, uid, item }) {
  * @param {string} [options.after] - After cursor
  * @param {number} [options.limit] - Items per page
  * @param {string} [options.userId] - User ID for read state
+ * @param {boolean} [options.showRead] - Whether to show read items (default: false)
  * @returns {Promise<object>} Timeline with items and paging
  */
 export async function getTimelineItems(application, channelId, options = {}) {
@@ -86,7 +87,12 @@ export async function getTimelineItems(application, channelId, options = {}) {
     typeof channelId === "string" ? new ObjectId(channelId) : channelId;
   const limit = parseLimit(options.limit);
 
+  // Base query - filter out read items unless showRead is true
   const baseQuery = { channelId: objectId };
+  if (options.userId && !options.showRead) {
+    baseQuery.readBy = { $ne: options.userId };
+  }
+
   const query = buildPaginationQuery({
     before: options.before,
     after: options.after,
@@ -256,6 +262,24 @@ export async function getItemsByUids(application, uids, userId) {
   return items.map((item) => transformToJf2(item, userId));
 }
 
+/**
+ * Count read items in a channel
+ * @param {object} application - Indiekit application
+ * @param {ObjectId|string} channelId - Channel ObjectId
+ * @param {string} userId - User ID
+ * @returns {Promise<number>} Number of read items
+ */
+export async function countReadItems(application, channelId, userId) {
+  const collection = getCollection(application);
+  const objectId =
+    typeof channelId === "string" ? new ObjectId(channelId) : channelId;
+
+  return collection.countDocuments({
+    channelId: objectId,
+    readBy: userId,
+  });
+}
+
 /**
  * Mark items as read
  * @param {object} application - Indiekit application