Feature suggestion: Day counters / milestone tracking in Proton Calendar

Proton Calendar currently only looks forward: events and appointments. I'd like to suggest adding a simple but powerful complementary feature — day counters, similar to apps like Daycounter.

What it would do:
- "Days since" a chosen date (e.g. company founded, quit smoking, contract start, sobriety, purchase date)
- "Days until" a future date (countdowns to renewals, deadlines, anniversaries)
- Optional reminders at milestones (100 days, 1 year, etc.)

Why it fits Proton:
1. It's calendar-native data — dates are already the core object of the app. No new data model needed, just a new view on existing events.
2. Privacy angle: these are often highly personal dates (health, habits, sobriety, relationships). Today users store them in third-party apps with unknown data practices. Proton's E2E encryption is a genuine differentiator here — this is exactly the kind of sensitive data people would prefer to keep inside the Proton ecosystem.
3. Retention & daily engagement: counters give users a reason to open the calendar daily, not only when they have meetings. It moves Proton Calendar from a utility to a personal dashboard.
4. Low complexity, high perceived value: it's essentially a recurring calculation + widget/list view, not a new product.

The result: Proton Calendar becomes more than an agenda — a private timeline of what matters in your life, protected by encryption. I'd happily beta test this.

Thanks for considering it.