The time column in session and timeline pickers had two alignment
issues causing the datetime to render partially or fully off-screen,
especially when a preview pane was active.

Per-item variable width: each row computed its own time column width
from format_time(timestamp), producing different widths for same-day
(e.g. '10:35') vs older entries (e.g. '09 Jun 2024 10:35'). Fixed by
using format_time(0) to derive the maximum column width from the
longest possible output (different-year format). Shorter time strings
are right-padded within the fixed column.

Separator double-counting: the +1 in time_width and debug_width was
intended for the separator between parts, but to_string() and
to_formatted_text() already add their own separators. This caused rows
to exceed item_width by 1-2 chars, pushing the time column past the
visible pane edge. Fixed by accounting for separators explicitly.

Unreliable fzf width_callback: the start:+transform callback read
FZF_PREVIEW_COLUMNS to compute list pane width, but this env var could
be 0 or absent at fzf start time. When missing, format_width fell back
to the full window width, formatting items much wider than the visible
list pane. Removed this mechanism in favor of the M.pick-level
format_width which already accounts for the preview split ratio.