Remove EntityRegistry Smart-Contract

[arrivets]

Motivation

The EntityRegistry contract is a thin Solidity shim — it validates
ownership / liveness / attribute charset, emits the EntityOperation event,
then forwards an OpRecord[] batch to the precompile. Profiling against the
direct-precompile baseline (just profile-create-compare) shows the
contract adds substantial wall-clock per tx for behavior the precompile is
already in the position to do natively. See commit 9670727
("feat(profiling): direct-precompile baseline + percentile timing") for
methodology.

Scope

• Reduce contracts/src/EntityRegistry.sol to an interface:
  • interface IEntityRegistry { function execute(Operation[]) external; }
  • keep the Operation / Attribute / Mime128 / Ident32 /
    BlockNumber32 structs, op-type constants, and the
    EntityOperation event signature — these are the SDK ABI surface.
  • delete all implementation (per-op handlers, ownership / liveness
    validation, internal mappings, precompile CALL).
• Drop the bytecode bake in crates/arkiv-genesis
  (entity_registry_runtime_code(), entity_registry_account(), the
  predeploy entry in genesis_alloc()).
• Move the deleted Solidity logic into the precompile
  (crates/arkiv-node/src/precompile.rs):
  • per-op validation (ownership, liveness, attribute charset)
  • EntityOperation event emission
  • OpRecord accumulation → direct dispatch into arkiv-entitydb
• Register the precompile at ENTITY_REGISTRY_ADDRESS (today
  ARKIV_PRECOMPILE_ADDRESS). Drop ARKIV_PRECOMPILE_ADDRESS. Callers'
  txs continue to target the same address with the same calldata.
• Replace the precompile's input.caller == ENTITY_REGISTRY_ADDRESS
  check with per-op authorization on input.caller directly:
  • CREATE: open to any EOA
  • SET_ATTRIBUTE / REMOVE_ATTRIBUTE / EXTEND_LIFETIME / CHANGE_OWNER /
    DELETE: input.caller must equal the entity's stored owner
    (DELETE additionally allowed for anyone after expiresAt, per Permissionless DELETE on expiry #90)
• Keep the DELEGATECALL / CALLCODE / STATICCALL guards — they're
  properties of how the call is made, not who makes it.

API compatibility

External ABI preserved — same execute(Operation[]) selector, same
EntityOperation event signature, same destination address. SDKs
(arkiv-bindings, arkiv-sdk-js) keep codegenning from
EntityRegistry.sol; nothing changes for callers.

Security posture

Identical. Database chains forbid arbitrary user-deployed contracts and
disable EIP-7702 (no delegated EOAs), so input.caller is by construction
always an EOA — the same value EntityRegistry's msg.sender resolves to,
one hop earlier. Trust chain becomes:

signed tx → EVM signature validation → input.caller → precompile

instead of:

signed tx → EVM signature validation → EntityRegistry's msg.sender
          → OpRecord.sender → precompile

One fewer trusted component, same guarantees.

Touch points

• crates/arkiv-node/src/precompile.rs (main locus — gains validation,
  per-op auth, event emission; registered at ENTITY_REGISTRY_ADDRESS)
• crates/arkiv-node/src/evm.rs (precompile registration address)
• contracts/src/EntityRegistry.sol (gutted to interface-only)
• crates/arkiv-genesis/src/lib.rs (drop runtime-code bake and the
  entity_registry_account predeploy; ENTITY_REGISTRY_ADDRESS constant
  kept and now refers to the precompile slot)
• e2e/ (existing tests should pass unchanged)
• justfile (contracts-build recipe can drop the artifact step if
  nothing else needs compiled bytecode)

Acceptance criteria

• All existing e2e tests pass without modification (ABI parity).
• just profile-create-compare shows the contract-routed and direct-
  precompile paths converge — they're now the same path.
• Per-op authorization tests: CREATE from any EOA succeeds; non-owner
  SET_ATTRIBUTE / DELETE / EXTEND_LIFETIME / CHANGE_OWNER reverts with
  the same error shape as today.
• DELEGATECALL / STATICCALL / value-bearing calls remain rejected.

Relation to #88 (fee system)

Independent but adjacent. With the contract gone, #87 ("Implement Fee
Function in EntityRegistry Precompile") lives in a precompile that's
already the single source of truth — no contract-side fee logic to
coordinate, no duplicate authorization layer to update. Best landed
before #87 to avoid churning the precompile while #87 is in flight.