feat: add custom calendar support via plist

[rantoniuk]

Problem

Clicking a calendar event in the Notch always opened Apple Calendar, ignoring the macOS Default Calendar App system setting (#1286).

This is alternative implementation to (#1288)

Root cause: EventModel.calendarAppURL() hardcoded the ical://ekevent/… URL scheme. This scheme is Apple Calendar's proprietary internal protocol — macOS never routes it to any third-party app, regardless of the system preference. The Default Calendar App setting only affects .ics file opens and webcal:// subscription URLs, not ical://.

Solution

Detection

The default calendar app is resolved at runtime by querying which application handles webcal:// links — the same signal macOS uses for the system
preference:

NSWorkspace.shared.urlForApplication(toOpen: URL(string: "webcal://x"))

Data-driven URL routing

A new bundled resource — CalendarAppURLSchemes.plist — maps each calendar app's bundle ID to a URL template. Two placeholders are supported:

Placeholder	Value
{id}	percent-encoded EKEvent.calendarItemIdentifier
{date}	ISO-8601 recurrence date prefix for Apple Calendar (/yyyy-MM-dd'T'HH:mm:ssZ), empty string for non-recurring events

Initial entries:

App	Bundle ID	Template
Apple Calendar	com.apple.iCal	ical://ekevent{date}/{id}?method=show&options=more
Fantastical	com.flexibits.fantastical2.mac	x-fantastical2://show?eventIdentifier={id}
BusyCal	com.busymac.busycal3	busycal://open?calendarItemIdentifier={id}

If the plist has no entry for the current default app, the code falls back to the original ical:// URL (Apple Calendar behaviour).

Adding support for a new calendar app

No Swift changes needed — just a one-line addition to the plist:

# 1. Find the bundle ID
mdls -name kMDItemCFBundleIdentifier /Applications/YourCalendar.app

# 2. Add to CalendarAppURLSchemes.plist:
# <key>com.example.yourcalendar</key>
# <string>yourcal://open?id={id}</string>

Known limitation

Microsoft Outlook for Mac is not supported: it does not register as a webcal:// handler (so it cannot be detected) and has no documented URL
scheme for opening an existing calendar event by identifier.