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/transit.clj

@@ -0,0 +1,32 @@
+(ns pocketbook.transit
+  "Transit encoding/decoding helpers for the HTTP wire format."
+  (:require [cognitect.transit :as t])
+  (:import [java.io ByteArrayInputStream ByteArrayOutputStream]))
+
+(defn encode
+  "Encode a Clojure value to a Transit+JSON byte array."
+  [v]
+  (let [out (ByteArrayOutputStream. 4096)
+        w   (t/writer out :json)]
+    (t/write w v)
+    (.toByteArray out)))
+
+(defn encode-str
+  "Encode a Clojure value to a Transit+JSON string."
+  [v]
+  (let [out (ByteArrayOutputStream. 4096)
+        w   (t/writer out :json)]
+    (t/write w v)
+    (.toString out "UTF-8")))
+
+(defn decode
+  "Decode a Transit+JSON byte array or input stream to a Clojure value."
+  [input]
+  (let [in (cond
+             (instance? ByteArrayInputStream input) input
+             (instance? java.io.InputStream input)  input
+             (bytes? input) (ByteArrayInputStream. input)
+             (string? input) (ByteArrayInputStream. (.getBytes ^String input "UTF-8"))
+             :else (throw (ex-info "Cannot decode, unsupported input type"
+                                   {:type (type input)})))]
+    (t/read (t/reader in :json))))