#481 Polish cascade-affected meetings table in postpone/reschedule prompt

- Drop the leading "#" index column; dailyNumber already serves as a
  stable per-row identifier.
- Replace the hard-coded amber background/border with the user's chosen
  alert accent via hexToRgba(accent, 0.12 / 0.45). Threaded `accent`
  through PostponeDialog → CascadePromptBlock so children don't read
  prefs directly. Both the loading and main prompt blocks track the
  accent; the rose blocked-by-midnight variant is intentionally kept.
- Render times as localized 12-hour with ص/م (AR) or AM/PM (EN) by
  reusing the shared formatTime helper instead of slicing "HH:mm".
- Drop now-unused i18n key cascadeColIndex from ar.json + en.json.
- Update the e2e test to match the 3-column schema (meeting#, title,
  times); kept the dailyNumber assertion in the first cell.

tsc clean. Cascade specs pass (Postpone by 10, Reschedule cascade,
Cascade prompt UI: Shift/Keep, no-followers fallthrough).

artifacts/tx-os/src/locales/en.json

@@ -1224,7 +1224,6 @@
       "cascadePromptHeader_one": "{{count}} later meeting on this day would be affected. Also shift it by {{minutesText}}?",
       "cascadePromptHeader_other": "{{count}} later meetings on this day would be affected. Also shift them by {{minutesText}}?",
       "cascadeListTitle": "Affected meetings:",
-      "cascadeColIndex": "#",
       "cascadeColMeetingNumber": "Meeting #",
       "cascadeColTitle": "Title",
       "cascadeColTimes": "From → To",