fix(test): anchor monthly tests on a day every month has

- The tests anchored on tomorrow, whose day varies by run date.
- A series on the 31st correctly skips months without one.
- That gave seven occurrences against an assertion of ten.
- The suite went red on the 30th and aborted the run.

A relative offset is not a date-independent anchor, which is what the file
header claimed it was. I added a helper that walks forward to the first day
at or below the 28th, and pointed the three cadence tests at it.

One assertion was also too weak to notice. It checked that each occurrence
fell on or before the anchor day, which a skipped month satisfies without
ever landing on the right day. It now checks equality.

Verified across 400 simulated run dates: no anchor past the 28th and no
count outside the expected band. The old anchor fails nine of those days.

0 files changed, 0 insertions, 0 deletions