Site: Expand Variant intro blog with Iceberg table-level details

[nssalian]

Changes

Discussed with @kevinjqliu offline about enhancing the blog for variant to have more Iceberg internal information in addition to the current content, so I:

• Covered schema, cross-file layout, snapshots, file formats, and statistics-based data skipping
• Did some cleanup to prepare for the next blog (shredding)

[uros-b]

The spec contradicts the final sentence. The "Bounds for Variant" section of format/spec.md defines a general mechanism (valid for shredded and unshredded Variant data), where the Variant column's manifest lower_bounds/upper_bounds entries are stored as Variant objects whose keys are normalized JSON path expressions (e.g. $['event_type']) and whose values are per-field min/max primitives. The spec explicitly states: "Including bounds for any field is optional", it does not restrict bounds to files written with shredding.

Suggested fix: Change the paragraph to reflect the practical picture, e.g.

For an unshredded Variant column, computing per-field bounds requires reading the raw value bytes, so writers typically record only counts. When a field is shredded into its own typed column, its Parquet statistics are available directly, and Iceberg can record lower and upper bounds for that field path in the manifest, stored as a Variant object whose keys are normalized JSON paths.