refactor(rundown): simplify gap and overlap accumulation

The gap/overlap detection is already a merge-intervals sweep: `latestEvent`
is the running max end and `getTimeFrom` is `start - maxEnd`. Making that
explicit collapses the branching around it.

- getTimeFrom: the three branches all returned the same subtraction
- totalDuration: the gap === 0 / gap > 0 / gap < 0 cases are all
  Math.max(duration + gap, 0), since duration is never negative

Same behaviour, no signature changes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016XSraCPafWbAg35gAFrtgH

packages/utils/src/date-utils/getTimeFrom.ts

@@ -17,17 +17,11 @@ export function getTimeFrom(
   const normalisedCurrentStart = current.timeStart + current.dayOffset * dayInMs;
   const normalisedPreviousEnd = previous.timeStart + previous.duration + previous.dayOffset * dayInMs;
 
-  // event is linked to previous
-  if (normalisedCurrentStart === normalisedPreviousEnd) {
-    return 0;
-  }
-
-  // event has a gap from previous
-  if (normalisedCurrentStart > normalisedPreviousEnd) {
-    // time from previous is difference between start and previous end
-    return normalisedCurrentStart - normalisedPreviousEnd;
-  }
-
-  // event overlaps with previous
+  /**
+   * The distance between the current start and the previous end
+   * - positive: there is a gap between the events
+   * - zero: the current event starts on the previous end
+   * - negative: the events overlap
+   */
   return normalisedCurrentStart - normalisedPreviousEnd;
 }