fix(leaderboard): explain global-rank gaps when filters are active

[Crystora]

Summary

The leaderboard # column shows each miner's global rank (position across all ~110 miners). When a filter is active — most visibly Eligibility = Eligible — the non-matching rows are hidden but the survivors keep their global rank numbers, so the column appears to "skip" (e.g. … 21, 22, 33, 107). The math is correct, but the gaps read as a bug.

This PR keeps the meaningful global rank and makes the gaps self-explanatory:

• Adds a one-line note above the table, shown only when a filter is active (eligibility tab, cohort, tracked-only, repo, or search): "Filtered view — the # column shows global rank across all miners, so hidden miners leave gaps in the numbering."
• Adds a tooltip on the # column header explaining the same.

Presentation-only — no sort/filter/ranking logic changed. The note lives in the shared toolbar, so it covers both list and card views. Implemented in MinersLeaderTable.tsx (the component rendered at /leaderboard); the issue's original reference to TopMinersTable.tsx / /top-miners is stale since that route now redirects to /leaderboard.

Related Issues

Fixes #1102

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

The gap (problem):

Before — no explanation, gaps look like a bug:

After — note added above the table explaining the global-rank gaps:

After (no filter) — note correctly hidden, ranks consecutive:

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run format and npm run lint:fix have been run
• npm run build passes
• Screenshots included for any UI/visual changes