feat: add prover and miner count time-series graphs

[zeroklaw]

Summary

Adds time-series graphs for Miner Count and Active Provers to the PoVW & Market Cycles tab, as requested in #42.

Changes

New API endpoint: /api/provers-history

• Fetches current prover count from explorer.boundless.network/api/base/provers/summary/1d
• Accumulates daily snapshots in KV (permanent, no TTL — historical data is immutable)
• Maps daily snapshots to epochs by averaging the prover counts over each 2-day epoch window
• Gracefully degrades to empty array when upstream is unavailable

Frontend: PovwCycles.tsx

• Extended EpochPoint interface with minerCount (from epoch data) and activeProvers (from prover-history API)
• Added ProversHistoryBucket interface and useEffect to fetch from /api/provers-history
• Updated mergeEpochData() to accept and merge prover history data
• Added Miner Count per Epoch AreaChart (blue #3b82f6) — shows num_participants per epoch over time
• Added Active Provers per Epoch AreaChart (green #22c55e) — shows averaged daily prover count per epoch
• Both charts only render when their respective data is available (> 0 values exist)

Closes #42

[github-actions]

Preview deployment

	URL
Latest commit	https://5b7873d8.boundless-profit-explorer.pages.dev
Branch alias	https://head.boundless-profit-explorer.pages.dev

The branch alias URL always points to the latest commit on this PR.

[mintybasil]

Miner data looks good, everything is working. For the "prover count" I think we have two related issues.

1. There is no graph shown
2. Data fetching seems limited

I'm assuming that issue 1 is caused by issue 2. AFAICT to fetch the prover count we are just loading explorer.boundless.network/api/base/provers/summary/1d. However this only provides a snapshot for a recent day. We need to backfill the data for all available epochs. In the explorer UI they have a stat Daily unique provers, which has exactly the data we need, perhaps you can try to find the API endpoint. This is part of the "stats" data, not a prover-specific endpoint.

Also - one potential miscommunication, we should be adding ONE graph with both counts.

[zeroklaw]

Thanks for the review! I've addressed both issues:

1. Fixed data fetching to use historical data

• Changed /api/provers-history to fetch from /base/stats endpoint (same as /api/market-stats)
• Now uses unique_provers_locking_requests field which provides historical daily unique prover counts
• Groups by epoch_number_start to map daily data to epochs (same approach as market-stats)
• This provides backfilled data for all available epochs, not just a single day snapshot

2. Combined into ONE graph

• Merged the "Miner Count per Epoch" and "Active Provers per Epoch" charts into a single chart titled "Miner & Prover Count per Epoch"
• Both metrics are now displayed together with a legend (blue for Miner Count, green for Active Provers)
• Chart only renders when either metric has data

Changes pushed to this branch. The prover count graph should now show historical data for all epochs.