Timeline: draw stage-period ranges from activities, milestones on top

Each stage-transition activity now becomes a horizontal range on its lane: start = the activity's date, end = the next activity with a higher stage rank, or extending to today if still in effect. Milestone date-field dots overlay on top of the ranges. Activity dots at each range start carry a tooltip with the activity subject. Added computeStageRanges in lib/stageRank.ts and switched DateTimeline to take activities directly (deriving both the rank resolver and the ranges internally). Wide year-spanning timelines now show their full extent even when no milestone dates have been entered.

components/ReportView.tsx

@@ -10,7 +10,7 @@ import type {
   StageSectionConfig,
 } from "@/types/form";
 import { STAGE_OPTION_GROUP_ID } from "@/config/form";
-import { STAGE_RANK, buildStageRankAtDate } from "@/lib/stageRank";
+import { STAGE_RANK } from "@/lib/stageRank";
 import { StageIcon } from "./StageIcon";
 import {
   FieldHistoryGroup,
@@ -121,7 +121,7 @@ export function ReportView({ config, cid, cs }: ReportViewProps) {
       <DateTimeline
         sections={config.sections}
         fieldHistory={data.fieldHistory}
-        stageRankAtDate={buildStageRankAtDate(data.activities)}
+        activities={data.activities}
       />
 
       {sectionsToRender.length === 0 ? (