fix(packages/app-store): exclude cancelled events and filter by date range in getAvailability

[zhyd1997]

Fixes two bugs in the ICS feed calendar service that caused false-positive busy times, resulting in "No available users found" errors for users with multiple calendar connections (e.g. Proton + Google Calendar via ICS feed).

1. Skip events with STATUS:CANCELLED - cancelled/declined meetings in ICS feeds were incorrectly counted as busy time, blocking otherwise free slots.

2. Filter non-recurring events by dateFrom/dateTo - unlike recurring events (which already filtered by range), non-recurring events were all returned regardless of whether they fell within the requested window.

Adds tests covering both behaviours.

https://claude.ai/code/session_01QKRwyaEnVrG3HLW1hRzGtG

What does this PR do?

• Fixes Booking an appointment in a free slot returns "The appointment could not be booked. No available users found. Can you try another time slot?" #23391 (GitHub issue number)
• Fixes CAL-6332 (Linear issue number - should be visible at the bottom of the GitHub issue description)

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[cubic-dev-ai]

No issues found across 2 files

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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