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.

README.md

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+# Pocketbook
+
+A Clojure-native synced atom. Offline-first key-value store with an `atom` interface that syncs to a SQLite-backed server over Transit.
+
+```clojure
+(def conn  (<! (pocketbook/open "my-app")))
+(def todos (pocketbook/synced-atom conn "todo" {:server "http://localhost:8090/sync"}))
+
+(swap! todos assoc "todo:1" {:text "Buy milk" :tags #{:groceries}})
+@todos  ;=> {"todo:1" {:text "Buy milk" :tags #{:groceries}}}
+```
+
+## What it does
+
+- **Preserves Clojure types**: keywords, sets, UUIDs, instants — no lossy JSON
+- **Works offline**: reads/writes hit IndexedDB immediately, syncs when online
+- **Atom interface**: `swap!`, `deref`, `add-watch` — works with Reagent, Rum, or raw CLJS
+- **~500 lines**: client (~300) + server (~200), no opaque dependencies
+
+## Quick start
+
+### Server
+
+```bash
+clj -M:server
+# or: clj -M:server 8090 my-data.db
+```
+
+Starts on `http://localhost:8090` with a SQLite file at `pocketbook.db`.
+
+### Client (CLJS)
+
+```clojure
+(ns my-app.core
+  (:require [pocketbook.core :as pb]
+            [cljs.core.async :refer [go <!]]))
+
+(go
+  (let [conn  (<! (pb/open "my-app"))
+        todos (pb/synced-atom conn "todo"
+                {:server "http://localhost:8090/sync"})]
+    (<! (pb/ready? todos))
+    (swap! todos assoc "todo:1" {:text "Buy milk" :done false})
+    (add-watch todos :log (fn [_ _ _ new] (println (count new) "todos")))))
+```
+
+## Architecture
+
+```
+Browser                              Server
+┌─────────────┐                     ┌──────────────┐
+│ SyncedAtom  │ ── Transit/HTTP ──▶ │ http-kit     │
+│  ↕ atom     │                     │  ↕ Transit   │
+│  ↕ IndexedDB│ ◀── Transit/HTTP ── │  ↕ Nippy     │
+│   (Transit) │                     │  ↕ SQLite    │
+└─────────────┘                     └──────────────┘
+```
+
+## Sync protocol
+
+- **Pull**: `GET /sync?group=todo&since=<epoch-ms>` — returns changed docs
+- **Push**: `POST /sync` — sends local changes with version numbers
+- **Conflicts**: server rejects stale writes, client accepts server value
+
+## Auth
+
+Optional token-based auth:
+
+```clojure
+(server/start! {:port 8090
+                :users {"alice" {:token "abc123" :groups #{"todo" "settings"}}
+                        "bob"   {:token "def456" :groups #{"todo"}}}})
+```
+
+Client passes token:
+
+```clojure
+(pb/synced-atom conn "todo" {:server "http://localhost:8090/sync"
+                              :token "abc123"})
+```
+
+## Dependencies
+
+| Layer  | Library | Purpose |
+|--------|---------|---------|
+| Server | next.jdbc + sqlite-jdbc | SQLite storage |
+| Server | nippy | Binary serialization |
+| Server | transit-clj | Wire format |
+| Server | http-kit | HTTP server |
+| Client | transit-cljs | Serialization (IDB + wire) |
+| Client | core.async | Sync coordination |
+
+## Tests
+
+```bash
+# All server tests
+clj -M:dev -e '(require (quote pocketbook.db-test) (quote pocketbook.transit-test) (quote pocketbook.server-test) (quote pocketbook.auth-test)) (clojure.test/run-all-tests #"pocketbook\..*")'
+```
+
+## License
+
+MIT