fix(longbridge): use native Decimal for order writes

[fanfpy]

Summary

• convert OpenAlice decimal.js values to the Longbridge SDK's native Decimal at submit/replace write boundaries
• cover quantity, limit price, trigger price, and trailing percent without converting through JavaScript number
• add regression tests that assert SDK Decimal class identity and exact decimal strings

Root cause

Order uses decimal.js, while Longbridge 4.0.5 N-API write options require instances of longbridge.Decimal. The previous as unknown as never casts only suppressed TypeScript errors, so the native binding failed to unwrap SubmitOrderOptions.submittedQuantity at runtime.

Verification

• pnpm vitest run services/uta/src/domain/trading/brokers/longbridge/LongbridgeBroker.spec.ts — 71/71 passed
• npx tsc --noEmit — passed
• pnpm -F @traderalice/uta-broker-longbridge typecheck — passed
• real native-binding probe — decimal.js source was not native; converted value was instanceof longbridge.Decimal; 123.4567890123456789 round-tripped exactly
• pnpm test — environment-blocked: 3253 passed, 62 unrelated failures under Node 25.8.1 from invalid localStorage support, missing Dugite embedded Git after download timeout, and Windows symlink EPERM
• live-paper — not run: no independently verified Longbridge paper account was available

Boundary touch

• trading

This external contribution targets dev as a proposal per CONTRIBUTING.md.

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