sdk: land the alloy-grade DX polish cluster

[mfw78]

Land the alloy-grade DX polish cluster as one umbrella: a typed venue fault mirror, a typestate order builder, uniform #[non_exhaustive], sealed extension traits, single-source vocabularies, and removal of the hand-copied golden bridges.

Why

Several DX-polish items have no owner: operator logs still {0:?}-format the venue error and the rate-limited{retry-after-ms} detail does not survive the fold; the bare 12-field order body literal is error-prone; the fault vocabulary is hand-mirrored in three places and the known table is duplicated; and each venue adapter hand-copies roughly 80 lines of golden bridge boilerplate. Consolidating them removes the last of the copy-paste and makes the surface alloy-grade. Part of milestone M3: Videre SDK, macros and DX. See docs/design/videre-split-plan.md and docs/design/issue-milestone-plan.md.

Scope

• Mirror VenueError to a VenueFault with Display, an IntoStaticStr label and From<bindings>, preserving retry-after-ms.
• Add an Order typestate builder to replace the bare 12-field OrderBody literal, plus CoW SellToken and BuyToken newtypes.
• Apply #[non_exhaustive] uniformly across the public error and label enums.
• Seal the extension traits (Host, HostFault, RuntimeTypes, Runtime, IntentPool) with a private Sealed supertrait.
• Derive the mirrored vocabularies from single-source consts, so the fault vocabulary and known table are emitted from one place.
• Remove the roughly 80-line *_to_golden bridge boilerplate.

Done when

• VenueError is mirrored to a Display and IntoStaticStr VenueFault that preserves retry-after-ms.
• The Order typestate builder and the sell and buy token newtypes exist.
• #[non_exhaustive] is uniform across the public error and label enums.
• The extension traits are sealed.
• The fault vocabulary and known table are emitted from single-source consts.
• The *_to_golden bridges are removed.

[mfw78]

Closing as already delivered, verified against origin/dev/m1@aec462a rather than taken on the issue text.

All six 'Done when' bullets are satisfied at tip. (1) VenueFault: crates/videre-sdk/src/faults.rs:29 pub enum VenueFault with thiserror::Error + IntoStaticStr + #[strum(serialize_all="snake_case")], From<VenueError> at faults.rs:57, and RateLimited { retry_after_ms: Option<u64> } whose Display renders ", retry after {ms} ms" — the hint survives; host side matches at crates/videre-host/src/bindings.rs:83-95 venue_error_message, so the {0:?} operator-log defect named in the Why is fixed too. (2) Typestate builder + newtypes: crates/cow-venue/src/order.rs:26 pub struct SellToken(pub Address) and :38 pub struct BuyToken(pub Address), driven as OrderBody::sell(SellToken(..), amount(42)).for_at_least(BuyToken(..), amount(41)) at crates/cow-venue/src/adapter.rs:560-561; order.rs uses core::marker::PhantomData for the typestate. (3) non_exhaustive: uniform on the public error/label enums — videre-sdk/src/keeper.rs:23 (Sweep), client.rs:302 (ClientError), body.rs:41 (BodyError), faults.rs:28 (VenueFault), plus 26 files carrying the attribute workspace-wide. (4) Sealed: nexum-sdk/src/host.rs:73-74 SealedHost/SealedHostFault with pub trait Host: sealed::SealedHost + ... at host.rs:421 and pub trait HostFault: sealed::SealedHostFault at :94; nexum-runtime/src/lib.rs:24-25 SealedRuntimeTypes/SealedRuntime, applied at preset.rs:35 and host/component/runtime_types.rs:18. (5) Single-source vocabularies: crates/nexum-world/src/lib.rs:19-116 derives EnumString/IntoStaticStr/VariantNames for the vocabularies and the whole ChainMethod table — landed by c57f729 (#551) and bbadf8a (#552). (6) git grep -n 'to_golden' origin/dev/m1 returns NOTHING — the ~80-line bridges are gone.

Closed manually because the M-train merges into the non-default dev/m1 branch, so nothing auto-closes.