Implement Governance SmartContract

[arrivets]

Refer to the arkiv fee spec: https://github.com/Arkiv-Network/arkiv-architecture/blob/main/arkiv/tokenomics/arkiv-fee-spec.md

Solidity contract storing all fee-function knobs (spec §4, §5), read by the
EntityRegistry precompile at execution time. Lives alongside
contracts/src/EntityRegistry.sol. Deployed as a predeploy from genesis.

State (all governance-writable)

• fee_multiplier (uint, bounded [0, fee_multiplier_max])
• usd_per_glm (uint, fixed-point — pick scale in PR)
• op_cost_create / delete / set_attr / remove_attr / extend / change_owner
• storage_rate_USD_per_KB_per_day
• fee_multiplier_max (deploy-time; change requires longer timelock)

Emit an event on every write.

Writes (per-update caps + timelock from spec §4, §9)

• setFeeMultiplier: ±X% per-update cap, short timelock
• setUsdPerGlm: ±20% per-update cap (spec §4), longer timelock, multi-sig
• setOpCost / setStorageRate: longer timelock
• setFeeMultiplierMax: longest timelock (rare change)

Access control

Decisions to make in this PR (escalate to #85 if unclear):

• Multi-sig implementation: Safe (Gnosis) at a known per-chain address, or
  custom. Default proposal: Safe.
• Timelock: separate contract (e.g., OZ TimelockController) between the
  multi-sig and this contract, or in-contract delay. Default proposal:
  separate TimelockController, one per cadence-tier.
• Role granularity: one role for everything, or split fast-moving knobs
  (fee_multiplier) from slow knobs (op_cost_*, storage_rate). Default
  proposal: two roles — FAST_GOVERNOR (fee_multiplier, usd_per_glm) and
  SLOW_GOVERNOR (everything else).

Acceptance tests must cover: unauthorized write reverts; authorized write
below cap succeeds after timelock; authorized write above cap reverts; write
from FAST_GOVERNOR to a SLOW_GOVERNOR-only knob reverts.

Genesis / deployment

The contract must exist from block 0 with initial values seeded, before the
first op can be charged.

• Predeploy address: pick a system-contract slot, consistent across chains
  (Kaolin testnet, dev, mainnet).
• Update crates/arkiv-genesis/src/lib.rs and chainspec/dev.base.json to
  include the predeploy bytecode + initial storage layout.
• Initial values: placeholders pending Calibrate Gas Constants #89; structure them so Calibrate Gas Constants #89's PR is a
  one-line constant swap.
• Owner / governance roles wired to the chain's governance multi-sig at launch.
• Verify Kaolin testnet bring-up uses the same path (no manual deploy step).

Reads

Public getters for every field, called by the precompile (#87) on every op.
Per spec §4 "display reconciliation": values must be queryable at any block
height so callers can verify before signing.

Out of scope

• Actual fee charging (precompile, Implement Fee Function in EntityRegistry Precompile #87)
• Oracle automation for usd_per_glm — manual governance writes in V1 (spec §4)
• Multi-sig deployment / signer onboarding — operational, not engineering

[marcos-golem]

I thinks this is really good.