feat: add n8n as a second workflow runtime alongside Node-RED

[manihagh]

Rebased from #38 onto v1.7.0 (after #34 reorganized the project structure).

What this adds

A second workflow runtime that runs alongside Node-RED. Solutions whose chain-declared executionEnvironment is N8nV1 are installed into n8n; every other solution continues to run on Node-RED exactly as before. Both runtimes share the same vote submission pipeline.

See docs/runtime-n8n.md for architecture details.

Review feedback from #38

All addressed in this branch:

• Runtime interface exposes getHealth(); health.ts is pure iteration across ALL_RUNTIMES
• startAllRuntimes / deleteAllFromAllRuntimes helpers in registry.ts
• SolutionIdentifier discriminated type used in routes/vote.ts and routes/worker-config.ts
• RUNTIME-N8N.md moved to docs/runtime-n8n.md

Tested end-to-end on mainnet

• vcc-1 installed into n8n via DEV_LOCAL_FLOW_OVERRIDES
• Vote submitted and settled on chain
• Graceful shutdown drains vote queue and terminates n8n child cleanly
• Node-RED flows continue working unchanged (NodeRedV1 default)

Configuration

Three new optional env vars (see .env.default):

• N8N_INTERNAL_PORT (default 5678)
• DEV_RUNTIME_OVERRIDES (dev-only)
• DEV_LOCAL_FLOW_OVERRIDES (dev-only)

When no solution uses executionEnvironment: N8nV1, the n8n child process still starts but stays idle. No manual setup required.

[azam-ismail]

need reset timer when n8nReadyPromise return before timeout