Unify localnet MPC node config template between guide and launch script

[Copilot]

The localnet automation path and manual guide had drifted to separate MPC node config templates, creating duplicate maintenance points. This change consolidates both paths onto the same TOML template used by the guide.

• Template consolidation

  • scripts/launch-localnet.sh now renders node config from docs/localnet/mpc-config.template.toml.
  • Removed the duplicate YAML template at docs/localnet/mpc-configs/config.yaml.template.

• Script startup path alignment

  • Replaced imperative mpc-node init + YAML runtime config flow with TOML-based startup via mpc-node start-with-config-file.
  • Keeps script behavior aligned with documented manual localnet flow.

• Operational effect

  • Localnet script and guide now share a single source of truth for MPC node configuration fields (near init, secrets, TEE, node/indexer ports, responder settings).

MPC_NODE_ID=$node_name \
NEAR_ACCOUNT_ID=$node_name \
NEAR_BOOT_NODES="$NODE_PUBKEY@127.0.0.1:24566" \
RPC_PORT=$((BASE_RPC_PORT + i)) \
INDEXER_PORT=$((BASE_INDEXER_PORT + i)) \
WEB_UI_PORT=$((BASE_WEB_UI_PORT + i)) \
MIGRATION_WEB_UI_PORT=$((BASE_MIGRATION_PORT + i)) \
PPROF_PORT=$((BASE_PPROF_PORT + i)) \
envsubst < docs/localnet/mpc-config.template.toml > ~/.near/$node_name/mpc-config.toml

RUST_LOG=info mpc-node start-with-config-file ~/.near/$node_name/mpc-config.toml