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 -->

packages/backend/server/src/plugins/calendar/providers/def.ts

@@ -1,4 +1,5 @@
 import { Inject, Injectable, Logger } from '@nestjs/common';
+import type { CalendarAccount } from '@prisma/client';
 
 import { CalendarProviderRequestError, Config, OnEvent } from '../../../base';
 import { CalendarProviderFactory } from './factory';
@@ -54,11 +55,17 @@ export interface CalendarProviderEvent {
 export interface CalendarProviderListEventsParams {
   accessToken: string;
   calendarId: string;
+  account?: CalendarAccount;
   timeMin?: string;
   timeMax?: string;
   syncToken?: string;
 }
 
+export interface CalendarProviderListCalendarsParams {
+  accessToken: string;
+  account?: CalendarAccount;
+}
+
 export interface CalendarProviderListEventsResult {
   events: CalendarProviderEvent[];
   nextSyncToken?: string;
@@ -97,7 +104,7 @@ export abstract class CalendarProvider {
     accessToken: string
   ): Promise<CalendarAccountProfile>;
   abstract listCalendars(
-    accessToken: string
+    params: CalendarProviderListCalendarsParams
   ): Promise<CalendarProviderCalendar[]>;
   abstract listEvents(
     params: CalendarProviderListEventsParams
@@ -117,12 +124,17 @@ export abstract class CalendarProvider {
   }
 
   get configured() {
-    return (
-      !!this.config &&
-      !!this.config.enabled &&
-      !!this.config.clientId &&
-      !!this.config.clientSecret
-    );
+    if (!this.config || !this.config.enabled) {
+      return false;
+    }
+    if ('clientId' in this.config || 'clientSecret' in this.config) {
+      return Boolean(this.config.clientId && this.config.clientSecret);
+    }
+    return true;
+  }
+
+  get supportsOAuth() {
+    return true;
   }
 
   @OnEvent('config.init')