feat(screener): add screener routes for market data filtering and pagination

[fadesany]

closes #63

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[Miracle656]

Nicely done — the screener route is well-structured and safe:

• Dynamic ORDER BY ${sortBy} ${order} is the one spot you can't parameterize, and you correctly allowlist both (allowedSortFields + asc/desc) before interpolation, so no injection.
• All filter values, the keyset cursor tuple, and limit go through $N placeholders.
• Keyset pagination with (sortBy, pair_key) row-value comparison + fetch-one-extra hasMore is the right approach, and the base64 cursor round-trips cleanly.

Minor (non-blocking) note: market_cap is aliased to the same expression as liquidity in screener_data, so filtering/sorting by market_cap behaves identically to liquidity. Fine as a placeholder, but worth a follow-up once real market-cap data exists.

The failing Typecheck & build check is the pre-existing src/webhookDispatcher.ts error on main (direction: string not assignable to ThresholdDirection) — unrelated to this PR; screener.ts adds no new type errors. Merging through it.