Verify or add a calendar year

The month-length table lives in data/calendar.csv. Verifying rows against a published panchang is the most useful contribution you can make. The full procedure, including the invariants enforced by tools/build_table.py, is in data/README.md.

In short:

1. Get a published panchang for the year (the national panchang is published at https://npns.gov.np).

2. Read every month boundary (the day the day number returns to 1), the Gregorian date printed for it, and the weekday of Baisakh 1.

3. Update the row, set evidence to verified, and cite the document in data/sources.toml with its URL and SHA-256 checksum.

4. Run uv run python tools/build_table.py to regenerate the table.

5. Add a calendar news fragment in changelog.d/ and open a pull request using the “New calendar year” or “Calendar discrepancy” template.

Changes to calendar data are released as a new minor version.