fix: verify and correct new operator behavior

[bearmug]

Summary

This PR verifies each of the 6 new operators end-to-end against the live TradingView scanner API and fixes the issues found.

Findings

Operator	API Status	Issue
empty → "empty"	Works	None — right: undefined correctly dropped by JSON.stringify
not_empty → "nempty"	Works	None
above_percent → "above%"	Wrong format documented	API requires [field_name, percent_float] — e.g. ["SMA200", 10] — NOT [percent, field]. Sending [10, "SMA200"] returns "type of percent must be float64" error
below_percent → "below%"	Wrong format documented	Same as above
has	Works on set-type fields	Only works on array/set fields like typespecs; returns "Unsupported string operation has" on string fields like sector
has_none_of	Works on set-type fields	Same caveat as has

Changes

src/api/types.ts

• Widen ScreenStocksInput.filter[].value type to include [string, number] tuple (for above_percent/below_percent)
• Make value optional at the type level (runtime validation in validateAndConvertFilters already handles the empty/not_empty special case)

src/index.ts

• Add all 6 new operators to the enum in every tool schema (screen_stocks, screen_forex, screen_crypto, screen_etf) — they were missing, so AI assistants using these tools had no way to discover them
• Update value field descriptions and examples to show the correct [field_name, percent] format for above_percent/below_percent and the array format for has/has_none_of

src/tests/screen.test.ts

• Add 10 new unit tests covering all 6 operators (conversion correctness, no-value behavior for empty/not_empty, value-required enforcement for other operators)
• Update validOperators list to include above_percent, below_percent, has, has_none_of (4 of the 6 new ones — empty/not_empty tested separately since they don't require a value)
• Test count: 84 → 94, all passing

Test plan

• npm run build passes (TypeScript clean)
• npm test — 94 tests, 0 failures
• Live API verified: empty/nempty return correct results (3 stocks vs 2235 stocks with dividend filter)
• Live API verified: above% with ["SMA200", 10.5] returns stocks with close > SMA200 * 1.105
• Live API verified: below% with ["SMA200", 10.5] returns 2078 large-caps below their SMA200 by 10.5%
• Live API verified: has with typespecs + ["common"] returns 206 results
• Live API verified: has_none_of with typespecs + ["preferred"] returns 290 results
• Live API verified: existing operators (in_range, greater, crosses_above) still work correctly