Incorrect Calculation of "Six Months Ago" for Memories Note on 2025-08-25

[shukebeta]

When calculating the "memories note" date, I noticed that on 2025-08-25, the date for "six months ago" was incorrectly calculated as 2025-02-26. This appears to be an error in the date calculation logic. Please investigate and correct the logic to ensure accurate "six months ago" calculations.

Steps to Reproduce:

1. Trigger the "memories note" calculation for the date 2025-08-25.
2. Observe that the result for "six months ago" is returned as 2025-02-26.

Expected Result:
The date calculated for "six months ago" from 2025-08-25 should be accurate according to calendar rules.

Actual Result:
The date is incorrectly calculated as 2025-02-26.

Additional Context:
Please review the date calculation logic, especially around month boundaries and leap years if applicable.