Add tabular-nums to figures and balance plan headings

Ten places in the app set a figure somebody reads as a column or watches change
— tool durations counting up, places-in-plan badges, the outstanding and
resolved counts, the overflow chip on the presence row, and the timestamps down
the transcript, a comment thread and a provenance line. Proportional digits are
different widths, so 2ms and 72ms put their figures in different places and a
column of them twitches as each lands. Tabular numerals cost nothing here; none
of these are prose.

Headings balance, so a two-line heading does not break 8/1 and read as a
mistake. They are short enough for the browser to weigh every break at once.

Paragraphs are left alone. `text-wrap: pretty` would guard the last line against
stranding a word, but the prose is inside a contenteditable and the browser
re-evaluates those lines on input, which is a reflow risk taken for a small
typographic gain.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>