chore: document date formatting scope and evaluate date-fns if requirements grow

Summary

formatToIST() in src/lib/utils.ts is a single-purpose formatter for the Asia/Kolkata timezone. It is currently sufficient but is a custom implementation with no tests.

Trigger for Action

If any of the following arise, adopt date-fns + date-fns-tz:

• Relative time display ("2 hours ago")
• Date arithmetic (add/subtract days, weeks)
• Multiple timezone support
• Date range calculations

Immediate Action

Add a comment above formatToIST() documenting the known limitation and the threshold for adopting a library:

// Single-purpose IST formatter. If date handling requirements grow (relative
// times, arithmetic, multiple timezones), replace with date-fns + date-fns-tz.

References

• date-fns: https://date-fns.org/ (MIT)
• date-fns-tz: https://github.com/marnusw/date-fns-tz (MIT)

Labels: chore, tech-debt