fix(whatsapp): pin protobufjs >=7.5.5 via npm overrides to clear 3 critical vulns (#19204)

The whatsapp-bridge pulls @whiskeysockets/baileys at a pinned git
commit whose transitive dep tree ships protobufjs <7.5.5, triggering
GHSA-xq3m-2v4x-88gg (critical, arbitrary code execution). npm audit
reported 3 cascading criticals: protobufjs, @whiskeysockets/libsignal-node
(pulls protobufjs), and baileys itself (effect rollup).

Fix: add npm overrides block pinning protobufjs to ^7.5.5. Deduplicates
to a single 7.5.6 copy at node_modules/protobufjs that both libsignal-node
and any other consumers resolve through normal module resolution.

Why not bump baileys: npm-published baileys@6.17.16 is deprecated by the
maintainers (wrong version), 7.0.0-rc.* still pulls the same vulnerable
libsignal-node, and upstream Baileys HEAD adds a 4th vuln (music-metadata).
The override is the minimal, behavior-preserving fix.

Validation:
- npm audit: 3 critical -> 0 vulnerabilities
- node -e "import('@whiskeysockets/baileys')" -> all 5 named exports
  (makeWASocket, useMultiFileAuthState, DisconnectReason,
  fetchLatestBaileysVersion, downloadMediaMessage) resolve
- node bridge.js loads all modules and reaches Express bind
  (exits only on EADDRINUSE because the live gateway owns :3000)
- Single deduped protobufjs@7.5.6 in the tree

scripts/whatsapp-bridge/package.json

@@ -12,5 +12,8 @@
     "express": "^4.21.0",
     "qrcode-terminal": "^0.12.0",
     "pino": "^9.0.0"
+  },
+  "overrides": {
+    "protobufjs": "^7.5.5"
   }
 }