iCal export: include day notes and untimed activities in calendar entries

[michidk]

Problem

The existing iCal export includes hotels or the whole trip, but:

1. Day notes are not included at all
2. Activities/places are excluded from the export

This means the calendar only shows a partial picture of the day — you still need to open TREK to see the full plan.

Proposal

Enhance the iCal export to also include:

• Day notes — added to the relevant day's calendar entry description
• Untimed activities/places — listed in the day's description even if they don't have a specific start/end time
• Notes & attractions with a time should have their own entries.

For example, a day's calendar entry could look like:

Summary: Day 3 — Rome
Description:
  09:00 Colosseum
  12:00 Lunch at Trattoria Da Enzo
  (no time) Vatican Museums
  (no time) Gelato at Giolitti

  Notes:
  - Remember to bring the Roma Pass
  - Vatican dress code: no bare shoulders

Untimed entries could either be grouped into a single all-day event per day, or appended to the description of the day's first timed entry.

Why this is useful

• The calendar becomes a complete daily itinerary, not just the timed slots
• Notes contain important reminders (dress codes, tickets, tips) that are easy to miss if only in TREK
• Untimed activities are often the bulk of a day's plan — excluding them defeats the purpose of the export

[mauriceboe]

The iCal export now includes day activities and notes:

• Timed activities are exported as individual calendar events with start/end times and location
• Untimed activities and day notes are grouped into an all-day summary event per day with a structured description

Live on dev, coming in the next release. 🚀