whatsapp: persist chats and messages across restarts (v8 / 2.2.0)

WhatsApp delivers a history sync at login, not on reconnect, so an in-memory
store left the connector blind after every process restart (23 in two weeks).
The store is now mirrored to store/, next to auth/ and bind-mounted the same
way.

Not SQLite: node:sqlite needs Node 22 (unflagged only from 24) and the runtime
image ships Debian trixie's nodejs = 20.19.2; better-sqlite3 is native and the
slim image has no toolchain. So an append-only JSONL log for messages plus a
debounced JSON snapshot for chats/contacts, both written tmp+rename so a crash
cannot truncate them. Compaction on load and every 500 appends keeps the log
from creeping upward.

Also fixes a pre-existing duplication bug: pushMessage appended unconditionally,
re-adding every message a history re-sync redelivered. It now returns false on a
known id and the message is skipped in both the transcript and the log.

MAX_MSGS_PER_CHAT 200 -> 500. logout deletes store/ with auth/, so re-linking a
different phone cannot inherit the previous account's history.

Data at rest: message text is now written to the user's bind-mounted home.
Nothing but session keys was persisted before.

Verified on skald-runtime:v4 with a seeded store: 751 lines with 50 duplicates,
a 700-message chat and a torn trailing line -> 701 loaded, compacted to 501, cap
applied, second run 501 -> 501 unchanged.

connectors/connectors.json

@@ -794,14 +794,14 @@
         "type": "qr"
       },
       "folder": "whatsapp",
-      "version": 7,
-      "version_string": "2.1.0",
+      "version": 8,
+      "version_string": "2.2.0",
       "version_release_date": "2026-08-23",
       "files": [
         {
           "path": "connector.json",
-          "sha256": "87bac98a524c604ca016a80b26200ae16aaee3926baecfe99e1c336833823307",
-          "size": 1485
+          "sha256": "7efc38c81915ecef2ecdd5bc16b4e3fbccc9ef735a5ae6262317b823a64d6f31",
+          "size": 1609
         },
         {
           "path": "icon_lg.png",
@@ -815,8 +815,8 @@
         },
         {
           "path": "index.js",
-          "sha256": "fa1f1c31c1f3b6b32df3de0a1175e1cb51a0417dce7e3aa52fa8655900dd2967",
-          "size": 29495
+          "sha256": "291a450714859e9f579bd2594bc6a5120daf17a9c77cf6c7cb1e59c64d5aa4f4",
+          "size": 33564
         },
         {
           "path": "package.json",