Longest Weekly Entry Display Below Total

Show how long the longest entry of the week was, under the week total.

Added a "Longest entry" line under This week on the Timesheet: pure thisWeekLongestMs (unrounded, a running entry counts to now) + test, UI, and Help. Quick gate green (195 tests). Visual check at desktop and mobile looks clean. PR #95 queued. Memory: none applied.