README: clearer structure, quick start, table schemas and methodology

Card: measurements in the pair rule, weekday pattern

low_days: days without a snapshot are judged with the snapshot that closes them (2026-01-31 is not low)

Card: short days

Card: renames, weekly rates, stale 30-day counts

Partial snapshots left out, stall windows take whole gaps, low_days only for shortfalls nothing makes up

Card: low_days, the low days nothing makes up

Document stall and rollback handling

Document datasets, Spaces and usage files

Link the site's own domain

Link the Space at its new address

Initial build: 2024-07-29 to 2026-10-02