The timeline windows a flat item list (month labels + chunked card rows)
with @tanstack/react-virtual over the shell's scroll container — single
scroll owner, bounded DOM at four-digit corpus sizes. Columns are
measured by a ResizeObserver so the row model and the painted grid never
disagree. Cards are compact-density: kind glyph, foreground title, one
muted meta line, condition pills, a download-only badge for attachment-
class formats, and a hover/focus selection checkbox above the whole-card
click target. In-flight and failed uploads share the same footprint with
a live progress ring and translated failure copy.
Plan-Task: W2-T2, W2-T4 (upload cards)
