[Bug]: Zooming out a tall diagram cuts off its top: the compacted container still centers the full-height SVG #1041

{
  "schema_version": 1,
  "diagram_type": "sequence",
  "meta": {
    "title": "Tall sequence zoom-out",
    "output": "tall-sequence.html",
    "quality_profile": "showcase"
  },
  "participants": [
    { "id": "client", "type": "external", "label": "Client" },
    { "id": "api", "type": "backend", "label": "API" },
    { "id": "db", "type": "database", "label": "DB" }
  ],
  "messages": [
    { "from": "client", "to": "api", "y": 200, "label": "request" },
    { "from": "api", "to": "db", "y": 290, "label": "query" },
    { "from": "db", "to": "api", "y": 380, "label": "rows", "variant": "return" },
    { "from": "api", "to": "client", "y": 470, "label": "reply", "variant": "return" },
    { "from": "client", "to": "api", "y": 560, "label": "request" },
    { "from": "api", "to": "db", "y": 650, "label": "query" },
    { "from": "db", "to": "api", "y": 740, "label": "rows", "variant": "return" },
    { "from": "api", "to": "client", "y": 830, "label": "reply", "variant": "return" },
    { "from": "client", "to": "api", "y": 920, "label": "request" },
    { "from": "api", "to": "db", "y": 1010, "label": "query" },
    { "from": "db", "to": "api", "y": 1100, "label": "rows", "variant": "return" },
    { "from": "api", "to": "client", "y": 1190, "label": "reply", "variant": "return" }
  ]
}

{
  "ok": true,
  "command": "deliver",
  "type": "sequence",
  "specification": { "sha256": "91d64073966091ddc2337deca36ed4919ce1aacec408cec4ce9946d6d8d13bca", "bytes": 1312 },
  "validation": { "checksPassed": 9, "checkCount": 9, "compositionProfile": "showcase", "compositionStatus": "pass", "errors": 0, "warnings": 0 }
}