refactor(clob): split the epoch-service god-object into focused modules (M4)

[drewstone]

Closes the last reasoned-deferred audit item (M4). Pure structural refactor —
zero behavior change.

Why

operator/src/clob.rs had grown to ~1.4k lines holding, in one impl Clob:
config parsing, the transport trait + its HTTP impl, every wire type, all
pool/finality state, the proposer driver, the verifier, and the axum surface.
One file, seven unrelated concerns.

What

Split into a clob/ module, one cohesive concern per file:

file	concern
config.rs	ClobConfig + SURPLUS_CLOB_* parsing
net.rs	the ClobNet transport trait + HTTP peer-list impl
wire.rs	JSON wire types (order / cancel / proposal / attestation)
pool.rs	admission, settled/cancelled finality sets + journal, snapshot, prune/evict
driver.rs	proposer side: match → H3 pre-sim → quorum → submit, on-chain client, membership reconcile
peer.rs	verifier side: attest + status
http.rs	axum router, handlers, env boot, background loops
mod.rs	Clob struct, constructors, shared accessors, re-exports

It's a move: the only non-mechanical change is bumping the handful of Clob
methods a sibling module now calls from private to pub(crate)/pub(super)
(snapshot, prune_filled, is_cancelled, load_finality, evict). The
public surface (crate::clob::{router, start_from_env, attest_deadline, Clob, ClobConfig, Wire*, ClobNet, HttpNet, cancel_digest, …}) is re-exported
unchanged, so mesh.rs and the integration tests didn't move a line.

A typed Attester newtype for the (Address, String) operator tuples was
deliberately left out — it ripples into mesh.rs and two test fixtures and
would bury this move-only diff. A follow-up if it earns its keep.

Verification

• Builds clean on both feature sets (default, and chain,mesh).
• Green: 13 operator unit + 4 clob_e2e + 1 mesh_clob + the matcher /
  settlement suites.
• Both anvil e2e proofs pass byte-for-byte against the refactored binary:
  the happy-path batch settle, and the H3 pre-sim adversarial grief
  (bookNonce unchanged, doomed buy evicted, seller's order survives).

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