Leaderboard period/metric tabs don't change sort or displayed values

Problem

In resources/views/leaderboard.stx the leaders derived value always .sort((a,b)=>b.totalDistance-a.totalDistance) regardless of the selected metric, and the podium/list always render totalDistance + ' mi'. Selecting Elevation/Activities (or the period tabs) only restyles the tab. The backend TerritoryLeaderboardAction (by area/count/conquests) isn't used here at all.

Acceptance

• Sort + display branch on the selected metric (distance/elevation/activities).
• Period tabs actually filter the window.
• Consider sourcing the territory leaderboard from the API.

Done: leaderboard now sorts by the selected metric, renders the right unit, and period tabs filter by date. Commit 0ec3272.