feat: basic caldav support (#14372)

fix #13531 

#### PR Dependency Tree


* **PR #14372** 👈

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**
* CalDAV calendar integration: link and sync CalDAV-compatible calendars
(discovery, listing, event sync).
* New UI flow and dialog to link CalDAV accounts with provider
selection, credentials, and display name.

* **API / Config**
* Server exposes CalDAV provider presets in config and new GraphQL
mutation to link CalDAV accounts.
  * New calendar config section for CalDAV with validation and defaults.

* **Tests**
  * Comprehensive CalDAV integration test suite added.

* **Chores**
* Removed analytics tokens from build configuration and reduced Cloud
E2E test shards.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.github/workflows/release-desktop-platform.yml

@@ -68,8 +68,6 @@ jobs:
       SENTRY_AUTH_TOKEN: ${{ secrets.SENTRY_AUTH_TOKEN }}
       SENTRY_DSN: ${{ secrets.SENTRY_DSN }}
       SENTRY_RELEASE: ${{ inputs.app_version }}
-      MIXPANEL_TOKEN: ${{ secrets.MIXPANEL_TOKEN }}
-      GA4_MEASUREMENT_ID: ${{ secrets.GA4_MEASUREMENT_ID }}
     steps:
       - uses: actions/checkout@v4