Add Recurring Tasks System

Description: Implement support for recurring tasks (daily, weekly, monthly)
Acceptance Criteria:

Add --recur flag to add command with frequency option

Automatically regenerate tasks based on recurrence rules

Show next occurrence in listings

Handle completion of recurring instances
Files Affected:

tasktrek

tasktrek-lib.sh

data/tasks.json (schema update)
Suggested Approach:
Store recurrence rules in task object. Add cron job or regeneration on command execution
Difficulty Level: ⭐️⭐️⭐️⭐️ (4/5)

Start by reading the tasktrek entry point and tasktrek-lib.sh, then inspect the current data/tasks.json schema. Trace how the add command, listings, and completion flow work before deciding how the stated recurrence criteria fit together. Done means the --recur option, regeneration behavior, next-occurrence display, and recurring-instance completion are all supported.

Written by the indexing model from the issue text.