feat(twap-monitor): build OrderCreation and submit via cow-api (BLEU-828)

[brunota20]

Summary

On `PollOutcome::Ready { order, signature }`:

1. `gpv2_to_order_data` maps the on-chain `bytes32` markers (`kind`, `sellTokenBalance`, `buyTokenBalance`) onto cowprotocol's typed enums via `from_contract_bytes`. Unknown markers skip the watch with a Warn log rather than ship a malformed body.
2. Wrap signature as `Signature::Eip1271` — ComposableCoW returns the orderbook wire form (raw verifier bytes; the orderbook prepends `from` before settlement).
3. `OrderCreation::from_signed_order_data` assembles the body. `from` is the watch owner; `app_data` is hard-coded to `EMPTY_APP_DATA_JSON`.
4. `serde_json::to_vec` → `cow_api::submit_order(chain_id, body)`.
5. On success, persist `submitted:{uid}` in local-store as an empty marker (presence is the receipt; suppresses double submits).

Scope notes

• `app_data` is fixed to `EMPTY_APP_DATA_JSON`. Orders that pin a real IPFS document fail `from_signed_order_data` (digest mismatch) and are skipped — resolving the document is a future concern.
• Submission errors are logged with status. BLEU-829 wires `OrderPostError::retry_hint` into this site so the backoff / drop decision becomes data-driven.
• `from` = watch owner (emitter of `ConditionalOrderCreated`); orderbook prepends it to the EIP-1271 blob during settlement.

Stacks on #4 (BLEU-827 polling).

Linear: BLEU-828. Ref ADR-0006 (modules build orders themselves).

Test plan

• `cargo test -p twap-monitor` — 24 host tests (3 BLEU-826 + 14 BLEU-827 + 7 BLEU-828: marker mapping incl. zero-receiver normalisation, unknown kind / balance rejection; build_order_creation happy path with serde round-trip; rejection of non-empty app_data and `from = ZERO`).
• `cargo clippy --target wasm32-wasip2 -p twap-monitor -- -Dwarnings`.
• `cargo clippy -p twap-monitor --tests -- -Dwarnings`.
• `cargo build --target wasm32-wasip2 --release -p twap-monitor` — 273 KB .wasm (was 215 KB; serde for OrderCreation + OrderData/Signature/SigningScheme + serde_with).
• End-to-end submit against Sepolia — pending BLEU-834 module.toml + a live conditional order.

[linear-code]

BLEU-828