refactor(timers): route the timer bars through the shared progress helper

[zachthedev]

shared/progress-bar.ts fills with Math.round. BlockTimer.ts,
BlockResetTimer.ts and WeeklyResetTimer.ts each carried a byte-identical
private makeTimerProgressBar that fills with Math.floor. Six other widgets
already use the shared helper, as do makeSliderBar and makeUsageProgressBar,
so floor was the only outlier in the repo.

The three copies are gone and all six call sites use the shared helper.

This changes rendered output. The bar shifts by one cell for roughly half of
all percentages, whenever the fill lands past the half-cell mark. BlockTimer's
own preview value is the clearest example: 73.9% of 32 cells is 23.648, so it
goes from 23 filled cells to 24. That widget already called the round-based
makeSliderBar for slider mode, so it was applying two rounding rules across its
own display modes.

Each of the three widgets gains a case pinning a value where floor and round
disagree (10% of 16, 73.9% of 32, 35% of 16). Putting Math.floor back in the
shared helper fails all three, so they are not retrofitted to current output.
Every pre-existing bar assertion is invariant under both rules, which is why none
of them needed touching.

The shared helper's cursor option stays inert here: all six timer call sites pass
no options, so cursorPos is -1 and the loop reproduces the old
'█'.repeat(filled) + '░'.repeat(width - filled) exactly. Bar length is still
exactly width, so truncation, powerline width math and flex separators see no
change.

Tested: bun run lint clean; bun test 1870 pass, plus the one
global-command-resolution failure main already has on this host.