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/core/package.json

@@ -65,7 +65,6 @@
     "graphemer": "^1.4.0",
     "graphql": "^16.9.0",
     "history": "^5.3.0",
-    "ical.js": "^2.1.0",
     "idb": "^8.0.0",
     "idb-keyval": "^6.2.2",
     "image-blob-reduce": "^4.1.0",