feat(client): support PolyV2 position orders

[cesarenaldi]

Summary

• accept exactly one of tokenID or positionID on limit and market order inputs
• use positionID to select Exchange V3 signing automatically while preserving existing token-order version selection
• carry the selected identifier through tick-size, order-book, fee, metadata, and order-construction paths
• retain the protocol-defined signed and wire field name tokenId
• document position-backed order placement

Why

PolyV2 markets expose position IDs instead of CTF token IDs. The client already supported Exchange V3 signing, but callers had to pass the position through tokenID and explicitly select version 3. The identifier field now serves as the protocol discriminator, matching the unified TypeScript SDK while retaining existing token-ID and Combo/RFQ compatibility.

Linear: DEV-549

Verification

• pnpm lint
• pnpm test — 303 tests
• pnpm build