whatsapp: fix history sync + session corruption, Baileys 7.0.0-rc14 (v7 / 2.1.0)

Diagnosed from the live server (two users, two accounts, one shared log).

- history sync was gated off entirely on Baileys 6.7.x: the library derives
  shouldSyncHistoryMessage from syncFullHistory when unset, and the connector
  shipped syncFullHistory: false. Now both are passed explicitly, so behaviour
  no longer depends on the resolved Baileys version. browser -> ['Mac OS', ...]
  because PLATFORM_MAP only grants a desktop-grade sync to Mac OS / Windows.
- reconnects leaked their socket, leaving two writers over auth/: no end(), no
  removeAllListeners(). ~15 reconnects/day produced 1422 Bad MAC lines, all on
  the account's own LID device 0. Added teardownSock(), per-socket generation
  guards, and a single-slot reconnect timer with exponential backoff.
- undecryptable messages (stubType CIPHERTEXT) were stored with empty text and
  rendered as blank transcript lines; now labelled and counted. Text-less
  protocol frames are dropped.
- fetchLatestBaileysVersion() ran on every reconnect; now cached for 6h.
- libsignal's direct console.error spam collapsed into one counted line, log
  lines tagged with the linked account, console.log redirected off stdout.

Baileys pinned ^6.7.9 -> 7.0.0-rc14 (the range resolved to 6.7.24 for one user
and 6.17.16 for the other). RC is ESM-only, so index.js is now ESM.

Verified on skald-runtime:v4 (Node 20.19.2): initialize, tools/list, status,
list_chats, version fetch, QR, and logout -> teardown -> single reconnect.

Remaining gap: the store is still in-memory only, so synced history is lost on
the next process restart.

connectors/whatsapp/fragment.json

@@ -5,7 +5,7 @@
   "scope": "user",
   "icon_small": "whatsapp/icon_sm.png",
   "icon_large": "whatsapp/icon_lg.png",
-  "user_description": "Send and read WhatsApp messages from your own linked account. Link via QR code \u2014 no browser needed.",
+  "user_description": "Send and read WhatsApp messages from your own linked account. Link via QR code — no browser needed.",
   "requires": [
     "NODE"
   ],
@@ -20,7 +20,7 @@
     "type": "qr"
   },
   "folder": "whatsapp",
-  "version": 6,
-  "version_string": "2.0.6",
-  "version_release_date": "2026-07-21"
-}
+  "version": 7,
+  "version_string": "2.1.0",
+  "version_release_date": "2026-08-23"
+}