feat(calendar): add comprehensive Calendar app support via CalDAV protocol

- Add complete CalDAV client implementation following NextCloud patterns
- Implement 11 comprehensive calendar MCP tools:
  * nc_calendar_list_calendars - list available calendars
  * nc_calendar_create_event - full event creation with recurrence, reminders, attendees
  * nc_calendar_list_events - enhanced with advanced filtering capabilities
  * nc_calendar_get_event - detailed event information retrieval
  * nc_calendar_update_event - comprehensive event modification
  * nc_calendar_delete_event - event removal
  * nc_calendar_create_meeting - quick meeting creation with smart defaults
  * nc_calendar_get_upcoming_events - upcoming events in next N days
  * nc_calendar_find_availability - intelligent scheduling with conflict detection
  * nc_calendar_bulk_operations - batch update/delete/move operations
  * nc_calendar_manage_calendar - calendar creation and management

- Add CalDAV and iCalendar dependencies to support calendar operations
- Implement comprehensive integration tests (11 test cases covering all scenarios)
- Update documentation with complete calendar tools reference and usage examples

Resolves #74

pyproject.toml

@@ -10,7 +10,9 @@ requires-python = ">=3.11"
 dependencies = [
     "mcp[cli] (>=1.10,<1.11)",
     "httpx (>=0.28.1,<0.29.0)",
-    "pillow (>=11.2.1,<12.0.0)"
+    "pillow (>=11.2.1,<12.0.0)",
+    "caldav (>=1.3.6,<2.0.0)",
+    "icalendar (>=6.0.0,<7.0.0)"
 ]
 
 [project.scripts]