feat: implement Pocketbook — a Clojure-native synced atom

Offline-first key-value store with atom interface (swap!, deref,
add-watch) that syncs to a SQLite-backed server over Transit.

Server (CLJ):
- SQLite storage with Nippy serialization preserving all Clojure types
- GET /sync?group=G&since=T pull endpoint with prefix-based groups
- POST /sync push endpoint with per-document version checking
- Conflict detection (stale write rejection)
- Token-based auth with per-user group access
- CORS support, soft deletes, purge compaction

Client (CLJS):
- IndexedDB wrapper with Transit serialization
- SyncedAtom implementing IAtom (IDeref, ISwap, IReset, IWatchable)
- Write-through to IndexedDB on every swap!
- Background sync loop (pull + push) with configurable interval
- Online/offline detection with reconnect sync
- Conflict resolution (accept server value)
- ready? channel for initial load
- Custom cache atom support (Reagent ratom compatible)

25 tests, 77 assertions across db, transit, server, and auth.

src/pocketbook/example.cljs

@@ -0,0 +1,75 @@
+(ns pocketbook.example
+  "Example: a simple todo app using Pocketbook."
+  (:require [pocketbook.core :as pb]
+            [cljs.core.async :refer [go <!]]))
+
+(defn- render-todos! [todos-atom]
+  (let [todos @todos-atom
+        container (js/document.getElementById "app")]
+    (set! (.-innerHTML container)
+      (str "<h1>Pocketbook Todos (" (count todos) ")</h1>"
+           "<div id='add-form'>"
+           "<input id='new-todo' type='text' placeholder='New todo...' />"
+           "<button id='add-btn'>Add</button>"
+           "</div>"
+           "<ul>"
+           (apply str
+             (for [[id doc] (sort-by key todos)]
+               (str "<li>"
+                    "<label>"
+                    "<input type='checkbox' data-id='" id "' "
+                    (when (:done doc) "checked") " /> "
+                    "<span" (when (:done doc) " style='text-decoration:line-through'") ">"
+                    (:text doc)
+                    "</span>"
+                    "</label>"
+                    " <button class='del-btn' data-id='" id "'>✕</button>"
+                    "</li>")))
+           "</ul>"
+           "<p style='color:#888;font-size:12px'>"
+           "Pending sync: " (pb/pending-count todos-atom)
+           "</p>"))))
+
+(defn- setup-handlers! [todos-atom]
+  ;; We re-setup after each render
+  (when-let [btn (js/document.getElementById "add-btn")]
+    (.addEventListener btn "click"
+      (fn [_]
+        (let [input (js/document.getElementById "new-todo")
+              text  (.-value input)]
+          (when (seq text)
+            (let [id (str "todo:" (random-uuid))]
+              (swap! todos-atom assoc id {:text text :done false})
+              (set! (.-value input) "")))))))
+  ;; Checkbox toggles
+  (doseq [cb (array-seq (.querySelectorAll js/document "input[type=checkbox]"))]
+    (.addEventListener cb "change"
+      (fn [e]
+        (let [id (.-id (.-dataset (.-target e)))]
+          (swap! todos-atom update-in [id :done] not)))))
+  ;; Delete buttons
+  (doseq [btn (array-seq (.querySelectorAll js/document ".del-btn"))]
+    (.addEventListener btn "click"
+      (fn [e]
+        (let [id (.-id (.-dataset (.-target e)))]
+          (swap! todos-atom dissoc id))))))
+
+(defn ^:export init []
+  (go
+    (let [conn   (<! (pb/open "pocketbook-example"))
+          todos  (pb/synced-atom conn "todo"
+                   {:server "http://localhost:8090/sync"})]
+      ;; Wait for initial load
+      (<! (pb/ready? todos))
+      ;; Render
+      (render-todos! todos)
+      (setup-handlers! todos)
+      ;; Re-render on changes
+      (add-watch todos :render
+        (fn [_ _ _ _]
+          (render-todos! todos)
+          (setup-handlers! todos)))
+      (js/console.log "Pocketbook example loaded!" (count @todos) "todos"))))
+
+;; Auto-init
+(init)