Recurring / DCA orders module

[DevMuhdishaq]

Description
Extend the orders module with dollar-cost-averaging (recurring) orders that execute a fixed-size swap at a set ledger interval — a strong educational feature.

Direction

• Add place_recurring_order(user, pair, amount, interval_secs, occurrences) to orders.rs.
• A permissionless execute_due_orders(order_id) (or keeper) executes when now >= next_run; advances next_run and decrements remaining occurrences.
• Respect rate limits, slippage, and pause state; emit events per execution.

Acceptance criteria

• A recurring order executes only when due and advances its schedule.
• Executes exactly occurrences times then auto-completes.
• cancel_order stops future executions.
• Insufficient balance skips/cancels gracefully with an event, no panic.
• Tests cover due/not-due, completion, and cancellation.

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[NteinPrecious]

i would like to work on this, can you assign it for me?

[grantfox-oss]

🦊 GrantFox — @NteinPrecious has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #219)
2. Your PR will be reviewed by the StelTade maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

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

@NteinPrecious's PR #232 was approved and merged by @DevMuhdishaq.

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

👏 Great work, @NteinPrecious! Keep contributing to StelTade.