feat(core): integrate google calendar sync (#14248)

fix #14170 
fix #13893 
fix #13673 
fix #13543 
fix #13308 
fix #7607




#### PR Dependency Tree


* **PR #14247**
  * **PR #14248** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Integrations panel in Account Settings to link/unlink calendar
providers.
  * Collapsible settings wrapper for improved layout.

* **Improvements**
* Calendar system reworked: per-account calendar groups, simplified
toggles with explicit Save, richer event display (multi-dot date
indicators), improved event time/title handling across journal views.

* **Localization**
* Added calendar keys: save-error, no-journal, no-calendar; removed
legacy duplicate-error keys.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/i18n/src/resources/de.json

@@ -2053,9 +2053,6 @@
   "com.affine.integration.calendar.unsubscribe": "Abonnement beenden",
   "com.affine.integration.calendar.new-title": "Kalender per URL hinzufügen",
   "com.affine.integration.calendar.new-url-label": "Kalender-URL",
-  "com.affine.integration.calendar.new-duplicate-error-title": "Dies ist ein doppelter Kalender",
-  "com.affine.integration.calendar.new-duplicate-error-content": "Dieses Kalender-Abonnement ist bereits im Konto der abonnierten Kalender vorhanden.",
-  "com.affine.integration.calendar.new-error": "Beim Hinzufügen des Kalenders ist ein Fehler aufgetreten",
   "com.affine.integration.calendar.all-day": "Ganztägig",
   "com.affine.integration.calendar.new-doc": "Neue Seite",
   "com.affine.integration.calendar.show-events": "Kalenderereignisse anzeigen",