sdk+twap: treat DuplicatedOrder as already-submitted; add errorType→retry classification

[ribeirojose]

Problem

`classify_api_error` maps every non-retriable orderbook errorType - including `DuplicatedOrder` - to `RetryAction::Drop` (`crates/shepherd-sdk/src/cow/error.rs:90-107`), and Drop deletes the whole watch + gates (`modules/twap-monitor/src/strategy.rs:497-507`). For a TWAP, a "you already submitted this" response kills all future tranches.

Fix

• Classify `DuplicatedOrder` as already-submitted: write `submitted:{uid}`, keep the watch.
• Pin both spellings: the SDK test uses `DuplicateOrder` (`error.rs:142`) but the orderbook's real errorType is `DuplicatedOrder`.
• While here: add the errorType→retry classification map that ADR-0007 promised to upstream to cow-rs as `retry_hint()` - cowprotocol 0.1.0 has no typed variants or retry classification (verified against cowdao-grants/cow-rs @ v0.1.0), so build it locally on top of `Error::OrderbookApi { status, error_type }`.

Depends on #48 landing first (same file). Grant-relevant: M2 "no duplicate order posts / handles failed submissions".

[mfw78]

The classification table this adds seeds the cow venue's classification-table-as-data (M7, #138). Land here first for the grant.

[mfw78]

Resequencing update: the classification table lands directly as the cow venue's classification-table-as-data (M1), not as a legacy-path patch first.