District competitions leaderboard page at /districts/id]/leaderboard

[clintjeff2]

Motivation

• Surface the weekly district competition scores that were previously computed only on-demand so users can see a per-district leaderboard and countdown to week reset.
• Provide a place to show previous-week snapshots (when available) and link from the city map/district overlay to the district leaderboard pages.

Description

• Add the new dynamic route for district leaderboards at app/districts/[id]/leaderboard/page.tsx which renders the top-10 agents for the current week with columns for rank, agent name, score, tasks completed this week, and district, and includes a responsive overflow table.
• Add a client CountdownTimer component at components/districts/countdown-timer.tsx that updates every second against the event endsAt timestamp.
• Add lib/gamification/district-leaderboard.ts to compute per-district top-10 results and to read JSON-backed previous-week snapshots from data/district-leaderboard-snapshots.json.
• Export/reuse helpers in lib/gamification/events.ts (getWeekBounds, formatDistrictScore, getAgentDistrictCompetitionScore, getWeeklyTasksCompleted) and adjust epoch/week calculation to align weekly boundaries; update the map overlay at components/open-stellar/district-event-overlay.tsx to link each district to its leaderboard.

Testing

• Ran npm run lint which reported pre-existing lint problems in unrelated files and did not pass (errors/warnings unrelated to this change).
• Ran npm test (Vitest): 82 test files and 533 tests ran successfully before the run failed overall due to a missing package (lru-cache) causing tests/skills/versioning.test.ts to fail; the new leaderboard code did not cause unit test regressions prior to that failure.
• Ran npx tsc --noEmit which failed due to missing dependencies (lru-cache and @wagmi/connectors) in the local environment rather than from the changes in this PR.

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Closes #185

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[clintjeff2]

@leocagli, review and merge.