fix(calendar): gate the enable-calendar prompt off on mobile

[gbirman]

Hides the "Enable calendar" prompt on phones behind a new enable-calendar-prompt-mobile flag, off by default everywhere including dev. The mobile custom-toast layout drops the body and close button, so the prompt lands as a bare title over the composer with no way to dismiss it.

Desktop is unchanged, and Settings > Email keeps a per-inbox "Enable calendar" button, so the action stays reachable while the prompt is off. Turn the flag on in PostHog once the mobile layout is fixed — #5407 is the alternative that fixes the layout instead.

[macro-application]

enable calendar option looks horrible on mobile

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Pro Plus

Run ID: 8112f74a-de53-4bd4-8d2c-77b7d25073e6

📥 Commits

Reviewing files that changed from the base of the PR and between 618726b and 8129f00.

📒 Files selected for processing (4)

• apps/web/src/features/auth/CalendarPermissionPrompt.tsx
• apps/web/src/features/calendar/use-calendar-ui-flag.test.ts
• apps/web/src/features/calendar/use-calendar-ui-flag.ts
• apps/web/src/lib/core/constant/featureFlags.ts

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📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added mobile-specific controls for displaying the “Enable calendar” prompt.
  • Calendar prompts now appear on mobile only when mobile support is enabled, while desktop behavior remains unchanged.

• Bug Fixes

  • Prevented calendar permission prompts from appearing in unsupported mobile layouts.

• Tests

  • Added coverage for desktop and mobile prompt display conditions.

Walkthrough

The calendar permission prompt now checks useCalendarPromptAllowed together with useCalendarUiFlag. Desktop devices remain eligible, while mobile devices require the new mobile calendar prompt feature flag. The change adds the flag constants, eligibility logic, and Vitest coverage for desktop and mobile flag states.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses conventional commits format, is 60 characters long, and clearly describes the mobile calendar prompt change.
Description check	✅ Passed	The description directly explains the mobile feature flag, affected prompt behavior, unchanged desktop behavior, and alternative access path.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[github-actions]

Preview: https://gbirman-macro-2754-disable-cal-df882k.preview.macro.com/app (15f92f2)