feat(kilo-pass): extend 2-month promo period by one week (#1067)

## Summary

Extends the Kilo Pass 2-month promo cutoff from March 14th to March
21st, 2026.

This change updates the `KILO_PASS_MONTHLY_FIRST_2_MONTHS_PROMO_CUTOFF`
constant in `src/lib/kilo-pass/constants.ts`.

## Verification

- Verified the change is a single-line date update matching the pattern
from PR #360.
- Confirmed the new date is exactly 7 days after the current cutoff.

## Visual Changes

N/A

## Reviewer Notes

N/A

Built for
[josh](https://kilo-code.slack.com/archives/C0A6SM2UG8N/p1773343569836179)
by [Kilo for Slack](https://kilo.ai/features/slack-integration)

Author: lambertjosh

src/lib/kilo-pass/constants.ts

@@ -12,7 +12,7 @@ export const KILO_PASS_FIRST_MONTH_PROMO_BONUS_PERCENT = 0.5;
 
 // First-time subscribers receive a 50% bonus for the first 2 months if they started
 // strictly before this cutoff.
-export const KILO_PASS_MONTHLY_FIRST_2_MONTHS_PROMO_CUTOFF = dayjs('2026-03-14T07:59:59Z').utc();
+export const KILO_PASS_MONTHLY_FIRST_2_MONTHS_PROMO_CUTOFF = dayjs('2026-03-21T07:59:59Z').utc();
 
 export const KILO_PASS_MONTHLY_FIRST_2_MONTHS_PROMO_BONUS_PERCENT = 0.5;