Proposal: add an offline arc-node check-config preflight command

[Kewe63]

Arc Node currently validates operator inputs across several binaries and configuration layers. Recent public issues have shown that invalid relay schemes, incompatible IPC/WebSocket settings, retry policies, rate and transaction-mix limits, and genesis values can reach startup or runtime before being rejected.

I would like to propose a read-only preflight command, tentatively:

arc-node check-config --config <path>

The command could:

• load configuration through the same parsing and validation paths used at startup;
• validate cross-field and nested invariants;
• normalize and inspect endpoint URLs without connecting to them;
• emit field-scoped diagnostics in human-readable and JSON formats;
• return a non-zero status for invalid configuration; and
• avoid network access, database writes, or other state changes.

An initial scope could cover node, consensus, remote-signer, genesis, and spammer configuration. CI could also run the same validator against the committed testnet and devnet configurations.

Would maintainers be interested in a shared preflight interface? If so, should it live in the main node CLI or in a separate operator utility?