refactor: replace core.async with promesa for all async operations

- Store protocol now returns promesa promises instead of core.async channels
- MemoryStore: `(p/resolved val)` replaces chan+put!+close! ceremony
- IDBStore: `p/create` with resolve/reject wraps IDB callbacks
- sync.cljc: CLJ uses `p/vthread`, CLJS returns native Promise chains
- core.cljc: `p/let` replaces go blocks, timer-based sync loop replaces
  go-loop+alts!, debounced push replaces kick channel
- Tests use `deref` with timeout on promesa promises
- Todomvc example uses `p/let` instead of go/<!

example/todomvc/pocketbook/todomvc.cljs

@@ -3,7 +3,7 @@
   (:require [pocketbook.core :as pb]
             [pocketbook.store.idb :as idb]
             [pocketbook.hiccup :refer [html]]
-            [cljs.core.async :refer [go <!]]
+            [promesa.core :as p]
             [clojure.string :as str]))
 
 ;; ---------------------------------------------------------------------------
@@ -232,9 +232,8 @@
 ;; ---------------------------------------------------------------------------
 
 (defn ^:export init []
-  (go
-    (let [store (<! (idb/open "pocketbook-todomvc"))
-          todos (pb/synced-atom store "todo"
+  (p/let [store (idb/open "pocketbook-todomvc")]
+    (let [todos (pb/synced-atom store "todo"
                   {:server "http://localhost:8090/sync"
                    :interval 15000})]
       (reset! !conn store)
@@ -248,7 +247,7 @@
       (.addEventListener js/window "online" (fn [_] (render!)))
       (.addEventListener js/window "offline" (fn [_] (render!)))
       ;; Wait for IDB — watch triggers render automatically
-      (<! (pb/ready? todos))
-      (js/console.log "🔶 Pocketbook TodoMVC loaded —" (count @todos) "todos"))))
+      (p/let [_ (pb/ready? todos)]
+        (js/console.log "🔶 Pocketbook TodoMVC loaded —" (count @todos) "todos")))))
 
 (init)