Fixed month-view rows that showed no week number at all.

Rows were identified by their first day number alone. Across a 28-day February
two candidate rows share that number — in March 2027, both Feb 21 / Mar 21 and
Feb 28 / Mar 28 — so the ambiguous rows were left blank. Rows are now matched on
their whole sequence of day numbers, and the genuinely indistinguishable ones are
placed by their offset from the rows that did resolve.

Fixed week numbers taking until the next scroll to appear. Relabelling now runs
on scroll and on in-place row recycling, coalesced into one pass per frame,
instead of only 300ms after rows were added or removed. The first pass no longer
waits half a second after the view opens.

Fixed a day-count comparison that could be swayed by the hour lost to daylight
saving.

Reading saved colours can no longer prevent week numbers from appearing.

Added a diagnostic attribute on the page's element so it is possible to
confirm the extension is running.