feat: real-time job status via Server-Sent Events

[orangecoding]

Summary

• Add a global SSE endpoint (GET /api/events) that broadcasts run:started and run:finished events to all connected browser tabs using a singleton EventEmitter bus
• Job list status badges update live (Running → Success/Failed) without any manual refresh, for both manually triggered and scheduler-triggered runs
• Run history panel auto-refreshes when a run finishes; reopening the same job's history always fetches fresh data

Changes

Server

• server/src/services/eventBus.js — singleton EventEmitter (with setMaxListeners(0) for unbounded SSE clients)
• server/src/scheduler/executor.js — emits run:started / run:finished on the bus
• server/src/app.js — new GET /api/events SSE route with socket-level cleanup, writableEnded guard, and X-Accel-Buffering: no for Nginx
• server/src/middleware/gatewayToken.js — accepts token from ?token= query param (EventSource cannot set custom headers)

Client

• client/src/hooks/useJobEvents.js — new hook: one EventSource per app lifetime, ref-based callbacks to avoid stale closures
• client/src/hooks/useJobs.js — adds updateRunStarted / updateRunFinished state setters
• client/src/hooks/useRunHistory.js — adds handleRunFinished for SSE-driven panel refresh
• client/src/App.jsx — lifts useRunHistory, wires useJobEvents
• client/src/components/runs/RunHistoryPanel.jsx — now a pure presentational component (data via props)

Test Plan

• Trigger a job manually — status badge changes to "Running" immediately, then "Success"/"Failed" when done
• Wait for a scheduled job to fire — badge updates without any user action
• Open run history panel, trigger a job — new run record appears automatically when it finishes
• Click history button for the same job twice — list refreshes on second click
• Kill and restart the dev server — browser auto-reconnects and resumes receiving events

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