0.4 release docs

[guillesd]

Documentation updates for DuckLake preview

Updates docs/preview/ to cover features shipped since the last stable release:

• Macros — new page documenting scalar and table macros; removes them from the unsupported features list
• Sorted tables — adds example setup, multiple sort keys, and expression-based sort keys (date_trunc, macros)
• Data inlining — restructured into Insertion Inlining and Deletion Inlining sections, each with internal catalog table schemas; documents variant inlining being DuckDB-only; covers
  auto_compact interaction and flush return values
• Data change feed — adds table_deletions and table_insertions functions
• Partial files — documents partial_max on ducklake_data_file and ducklake_delete_file; adds partial data file and partial deletion file concepts to merge and flush docs
• Compaction — documents auto_compact option and which tables are included in whole-lake/schema compaction calls; adds rewrite_data_files page
• Spec tables — new pages for ducklake_macro, ducklake_macro_impl, ducklake_macro_parameters, ducklake_sort_info, ducklake_sort_expression, ducklake_file_variant_stats; updates
  overview.md table count and schema script
• Configuration — corrects auto_compact description; documents new options
• scripts/update_docs.py — new automation script that fetches linked PRs from duckdb/ducklake and invokes Claude Code to draft doc changes