Icebird SQL

[platypii]

Adds in-browser SQL querying to the Icebird demo, replacing the single-table viewer with a query editor that resolves table identifiers against the database URL.

• SQL editor with syntax highlighting and error positions (HighlightedTextArea, sqlHighlight.ts)
• squirrelingDataFrame wires squirreling's SQL engine to a HighTable DataFrame, with lazy per-table iceberg loading via icebergDataSource
• Snapshot slider moved to the header and now anchored to the first table referenced in the query; pinned dataSources cached per snapshot
• URL routing moved from per-table to per-database; tables come from the SQL
• Show iceberg column types in the table header
• Sidebar style refresh
• Minor dep bumps (hightable, hyparquet) and CSS cleanup across sibling demos