update UDF to account for different Nova variants

[jaredsnyder]

There are two layouts with the Nova breakpoints: Sections and Grid. We want to make the distinction to make it easier to track changes. The biggest risk is that it will break the forecast content inputs table, but it will have not effect as presently constituted

[github-actions]

This PR splits the single NOVA layout value emitted by newtab.determine_grid_layout_v1 into NOVA_SECTION and NOVA_GRID (based on is_section), updates newtab.determine_tiles_per_row_v1 to match on both new values, and updates the tests and READMEs accordingly.

The core logic and CASE ordering are correct, and the tiles-per-row breakpoints are shared between both Nova variants as documented. I confirmed no other query in the repo hardcodes the old 'NOVA' literal, and the two consuming views (newtab_visits_daily, newtab_component_content) don't branch on it, so the rename is safe for downstream consumers. Two minor items are noted inline.

[scholtzan]

Integration report

• View full diff, if available (SQL + DAGs) (requires private-bigquery-etl access)
• Private CI run
• Bigeye monitoring dry-run: ✅ plan clean — view plan (requires private-bigquery-etl access)