feat: add Gmail Pub/Sub watcher for inbound email automation

New ChannelAdapter that monitors Gmail via Google Cloud Pub/Sub push
notifications with polling fallback. Supports OAuth2 auth, configurable
watch labels, template rendering with email metadata placeholders
(from, to, subject, snippet, date, id, labels).

Wired into daemon lifecycle and gateway (POST /gmail/push endpoint).
Includes 16 tests covering auth, templates, push notifications, and
channel routing.

package.json

@@ -50,6 +50,7 @@
     "commander": "^14.0.3",
     "croner": "^10.0.1",
     "discord.js": "^14.25.1",
+    "googleapis": "^148.0.0",
     "grammy": "^1.35.0",
     "ink": "^6.0.0",
     "ink-text-input": "^6.0.0",