feat(ranking): unify & fix pagination

[ZephyrNova47]

Add pagination for Contest Ranking tab

Description

Implement server-side pagination for the Ranking tab in contests. The pagination uses the canonical ?page= query parameter and renders once at the bottom of the table (no duplicate pager at the top). The default page size is 200 users per page.

Type of change: New feature

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What

This PR introduces pagination to the contest Ranking page and ensures it integrates cleanly with the existing auto-refresh and filtering behaviors.

• Server-side pagination

  • Uses the standard ?page= query parameter (e.g., /contest/<key>/ranking/?page=2).
  • Page size: 200 users per page.
  • Compatible with all existing query parameters (e.g., show_virtual, filters).

• Template changes

  • Wrap the ranking table in #rank-partial and include common/pagination.html once at the bottom.
  • Hide any pagination that might appear inside the partial:

    #rank-partial .pagination,
    #rank-partial nav.pagination,
    #rank-partial ul.pagination { display: none !important; }

  • Use the default site pagination but restyle it to match the previous black-button appearance (via CSS only).

• JavaScript changes

  • The periodic AJAX refresh now only replaces #ranking-table, avoiding overwriting the bottom pagination bar.
  • After each refresh, pagination inside the partial (if present) is removed.
  • Query-string parameters are preserved across reloads and when toggling “Show virtual participations”.

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Why

• Ranking pages with hundreds/thousands of participants are heavy to render and scroll.
• Pagination improves performance, accessibility, and usability.
• Keeping a single, consistent pager at the bottom avoids visual noise and accidental routing differences.

Fixes: N/A (feature work)

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How Has This Been Tested?

Environment

• Local dev server (DEBUG=True), MariaDB.
• Contest key: seed-test-0001.
• Seeded ~1000+ real participations with submissions.

Steps

1. Open /contest/seed-test-0001/ranking/ and confirm:
   • Only one pagination bar is visible (at the bottom).
   • Current page is highlighted.
   • First/Prev/Next/Last buttons work and keep the ?page= format.
2. Click into specific pages:
   • Direct links like ?page=2, ?page=5, etc. load correctly.
   • Deep links reload to the right page after refresh.
3. Verify query string preservation:
   • Toggle Show virtual participations and confirm the selection persists when paging and refreshing.
   • If additional filters are active, ensure they remain applied across pages.
4. Wait for the auto refresh (10s) and confirm:
   • Ranking table updates.
   • Bottom pager stays intact (not duplicated or removed).
5. CSV export (if enabled for non-ICPC):
   • Works on the current page view and ignores hidden rows.
6. Visual check:
   • Pager matches the “black button” look & feel via CSS (no custom routing).

Expected Results

• All pager links point to ?page=<n> and work correctly.
• No top pager remains; only the single bottom pager is visible.
• No regressions in tooltips, organization filter, or admin actions.

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Checklist

• I have explained the purpose of this PR.
• I have performed a self-review of my own code.
• I have commented code where helpful (templates/JS).
• I have made corresponding documentation / in-code notes where relevant.
• No breaking changes to URLs; uses canonical ?page= format.
• Verified behavior with 500+ participants and periodic refresh.
• Screenshots attached in the PR (if applicable).

By submitting this pull request, I confirm that my contribution is made under the terms of the AGPL-3.0 License.

[leduythuccs]

This seem big, we will revisit it later