Fix task scheduling for recurring tasks

[dkhalife]

• fix type
• rename enum
• new model for storing recurrence
• adjust data type to int array in sql
• calculate next occurrence

[Copilot]

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• go.mod: Language not supported

Comments suppressed due to low confidence (3)

internal/models/task/task.go:11

• The constant name 'FrequancyTypeOnce' is misspelled. It should be 'FrequencyTypeOnce'.

FrequancyTypeOnce          FrequencyType = "once"

internal/models/task/task.go:12

• [nitpick] The constant 'RepeatOnce' is not consistent with the naming convention used for other constants. Consider renaming it to 'FrequencyTypeOnce'.

RepeatOnce    = "once"

internal/services/planner/planner.go:7

• task.NextDueDate could potentially be nil, leading to a runtime panic. Add a nil check before dereferencing.

ScheduledFor: *task.NextDueDate,