Add media metadata support to event bus

[dellis317]

Summary

• Event bus events can now carry media attachments (image/audio/video) via metadata.media[]
• Media flows through publish, result, and SSE endpoints unchanged
• EventBus expanded view renders image/audio/video inline in log entries
• Aligns media metadata format with BSOffice notification system

Media Metadata Convention

{
  "metadata": {
    "media": [
      {
        "type": "image|audio|video",
        "url": "https://...",
        "mimeType": "image/png",
        "label": "Screenshot",
        "duration": 45,
        "source": "provocations"
      }
    ]
  }
}

Shorthand fields also supported by BSOffice: imageUrl, audioUrl, videoUrl.

Changes

• server/routes.ts: Result endpoint accepts metadata param, passes media through to eventBusLog and SSE events. Publish endpoint carries media to log entries. New API-key document metadata endpoint.
• EventBusExpandedView.tsx: Renders image (click to open), audio (controls), video (controls) inline in expanded log entries. Media type icons shown as badges on collapsed rows.
• useFlowCanvas.ts: eventBusLog type extended with optional media field.

Test plan

• Publish an event with metadata.media containing an image URL — verify it shows in listen node's log
• Post a result with metadata.media containing an audio URL — verify audio controls render in expanded view
• Verify SSE subscribers receive media metadata in event payload
• Verify backwards compatibility — events without media still work normally

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