[chain] Make FlowChain private/local L1 runtime runnable #99

Objective

Turn the existing Rust deterministic devnet into the runnable private/local L1 runtime for second-computer validation. Extend crates/flowmemory-devnet/; do not create a second runtime.

Worktree

E:\FlowMemory\flowmemory-chain on agent/full-l1-runtime.

Allowed folders

• crates/flowmemory-devnet/
• devnet/
• infra/scripts/ for runtime wrappers
• package.json / lockfile only for root orchestration commands
• docs/LOCAL_DEVNET.md
• FlowChain acceptance/setup docs only for evidence

Acceptance criteria

• A local node can run for at least 10 blocks and keep state on disk.
• Transactions for AgentAccount, ModelPassport, WorkReceipt, ArtifactAvailabilityProof, VerifierModule, VerifierReport, MemoryCell, Challenge, FinalityReceipt, and local test-unit balance/faucet records can be submitted and included.
• State survives restart and export/import still works.
• One-node smoke passes; two-node or multi-process smoke either passes or clearly marks LAN mode as not exposed while proving deterministic reconciliation.
• Existing deterministic fixture/demo behavior remains green.
• Handoff files or API-ready state are documented for control-plane and dashboard agents.
• Checks include cargo test --manifest-path crates/flowmemory-devnet/Cargo.toml and git diff --check.

Out of scope

Production consensus, tokenomics, public validators, production bridge, and mainnet claims.