good first issue: add explicit return types to lib/recurring.ts's exported functions

[Austinaminu2]

Description

Several exported functions in `lib/recurring.ts` (`saveRecurringRule` at line 27, `removeRecurringRule` at line 34, `buildNextRunAt` at line 46, `createRenewalPreset` at line 51) rely on inferred return types instead of explicit annotations, unlike `getRecurringRules(): RecurringRule[]` in the same file which already has one.

Location

`lib/recurring.ts:27, 34, 46, 51`

Task

Add explicit return type annotations to each of these functions, matching the existing convention set by `getRecurringRules()`.

Good for newcomers because

Small, mechanical type-annotation additions with an existing convention in the same file to follow.

[DingiDinigi]

HI I am able to handle this issue perfectly. I would drop a good PR once I'm done, please assign to me.

[ugoocreates-pixel]

@ugoocreates-pixel has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

So based on this description, with my experience, this shouldn't be an issue. I ask that you assign me to this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ugoocreates-pixel to this issue.

[abore9769]

@abore9769 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would like to take on this issue

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Congratulations, @abore9769! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@abore9769's PR #452 was approved and merged by @Austinaminu2.

🏆 @abore9769: You earned 35 FoxPoints for this contribution! Your current tier: Builder (1,009 total points). Track your full progress on GrantFox.

👏 Great work, @abore9769! Keep contributing to FlowwStar.

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This issue has been completed by @abore9769 as part of the Stellar Wave Program's 7th Wave 🥳

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