feat(schema): restructure log output format to match proto schema

[brucearctor]

Summary

Change the default JSON wire format to align with the proto schema structure. This is the primary breaking change in v3.0.0.

Current Format (v2.x — flat)

{
  "target": "button#submit",
  "pageUrl": "https://example.com",
  "userAgent": "Mozilla/5.0...",
  "clientTime": 1720800000000,
  "type": "click",
  "logType": "raw",
  "userId": "user123",
  "sessionId": "sess-abc",
  "attributes": { "data-count": 5 }
}

New Format (v3.0 — proto-aligned)

{
  "metadata": {
    "pageUrl": "https://example.com",
    "userAgent": "Mozilla/5.0...",
    "clientTime": 1720800000000,
    "userId": "user123",
    "sessionId": "sess-abc",
    "screenResolution": { "width": 1920, "height": 1080 }
  },
  "target": "button#submit",
  "eventType": "click",
  "userAction": true,
  "attributes": { "data-count": "5" }
}

Key Changes

• Shared fields grouped under metadata object
• type → eventType
• scrnRes → screenResolution (inside metadata)
• attributes values are always strings (no JSON.parse)
• logType field moves to envelope level

Depends On

• feat(schema): wire proto-generated types into packageLogs.ts #142 (wire proto types into packageLogs)
• feat(export): introduce LogExporter interface #139 (LogExporter interface — enables legacy format fallback)