Zenodo analysis: material category section empty due to PQG schema change

[rdhyee]

Problem

The Material Category Analysis section on tutorials/zenodo_isamples_analysis.qmd shows empty results after the column alias fix in PR #56.

Root cause

The Jan 2026 wide parquet (isamples_202601_wide_h3.parquet) stores material categories as p__has_material_category BIGINT[] — an array of row IDs (foreign keys) pointing to IdentifiedConcept nodes in the narrow format. The old export format had has_material_category as a plain string ("rock", "sediment", etc.).

The current fix maps has_material_category to NULL so the page loads without errors, but the material breakdown charts are empty.

Fix options

1. Pre-compute a lookup table in a small parquet file mapping row IDs → concept labels (similar to facet_summaries.parquet), and join at query time
2. Add denormalized string columns to a future wide parquet build (e.g., has_material_category_label VARCHAR)
3. Rewrite queries to join wide + narrow at runtime (expensive for browser-based DuckDB-WASM)

Option 1 is probably the best balance of effort vs. result.

Affected sections

• Section 9: Material Category Analysis (bar chart, drill-down by source)
• Any query referencing has_material_category as a string

Context

• PR Fix broken tutorial pages: explorer and zenodo analysis #56 fixed the page from completely broken → mostly working
• Geographic analysis, source collection, regional distribution, world map, and viewport map all work
• Only the material category breakdown is missing