fix: editable decrypt + windows realtime wake (v0.7.1)

Edit message decrypt:
- handleUpdate in useConversationMessages now refetches the canonical row
  via REST after a realtime UPDATE instead of trusting the realtime
  payload's bytea encoding. Same pattern as handleInsert — base64 vs
  `\x…` hex serialisation varies across supabase/postgrest versions and
  was silently producing undecryptable ciphertext for edited messages
  on the receiver side

Windows WebView2 background throttling:
- ConversationsContext, useFriendships and useConversationMessages now
  listen for visibilitychange / focus / online events and trigger both a
  fresh REST refresh and a best-effort channel.subscribe() on wake.
  WebView2 aggressively throttles background WebSockets and was dropping
  realtime events entirely while the window was minimised, so new
  messages and friend acceptances only surfaced after a manual reload

Bump tauri version 0.7.0 -> 0.7.1

apps/desktop/src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "ChatApp",
-  "version": "0.7.0",
+  "version": "0.7.1",
   "identifier": "com.meinname.chatapp",
   "build": {
     "beforeDevCommand": "pnpm vite:dev",