feat: standardize API typing and input variants for v0.3 gate #7

[TDamiao]

Summary

• add explicit public types for candle inputs and OHLCV object variants
• add a public API wrapper layer (src/api.ts) so core indicators accept consistent input styles
• support both long candle keys (open/high/low/close/volume/time) and aliases (o/h/l/c/v/t)
• centralize actionable numeric/input validation messaging
• document typing/input variants in README and add contract tests for both styles

Validation

• npm.cmd run build
• node --test --test-concurrency=1 --test-isolation=none test/contracts.test.mjs
• node --test --test-concurrency=1 --test-isolation=none test/golden.test.mjs

Notes

• In this sandbox, npm test with default isolation fails with spawn EPERM; test commands above pass with --test-isolation=none.

Closes #7