fix(calendar): correct ICS event formatting and time zone usage

[Gorlesunilkumar]

The ICS event file has been updated to follow proper RFC 5545 formatting and improve compatibility with calendar applications.

Changes

• Replaced the empty DESCRIPTION field with a valid value
• Unified DTSTART and DTEND to both use TZID=Europe/Berlin for consistent time zone handling
• Corrected the event duration (09:00–10:00 Berlin time)
• Removed unnecessary blank lines to avoid parsing inconsistencies
• Kept the full VTIMEZONE block to ensure compatibility with Nextcloud, Google Calendar, and iOS

Why

These adjustments improve interoperability with various calendar clients and prevent potential parsing issues caused by mixed time formats or empty fields.

Testing

The change updates only static test assets. No functional logic was modified.

• [x] Tests not needed (data file correction only)

[Gorlesunilkumar]

@alperozturk96 Review and merge

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