Create Tutorials landing page

[rdhyee]

Context

Hana's April wireframe includes a dedicated Tutorials landing page that doesn't exist on the current site. Currently tutorials are only accessible via the sidebar.

Wireframe shows

A page with:

• Header: "How to Use iSamples" / subtitle about exploring 6.7M samples
• Tutorial table with columns: Tutorial name, What You'll Learn
  • Interactive Explorer — search/filter with faceted search, 3D globe
  • Deep-Dive Analysis — comprehensive DuckDB-WASM analysis with Observable JS
  • 3D Globe Visualization — Cesium-based visualization
  • Technical: Narrow vs Wide — schema comparison and performance benchmarks
• Data Sources section explaining geoparquet + no-server approach
• Why Browser-Based? section with benefits (universal access, fast analysis, memory efficient)

Implementation

• New tutorials/index.qmd page
• Link from How to Use dropdown as "Overview"
• Table with links to each tutorial .qmd

Figma reference

Tutorials frame — "Tutorials" frame in Mock Up canvas

[rdhyee]

Completed in PR #93 (tutorials landing page with data tables and tutorial index).