chore(spec): auto-polish facet-grid (#6512)

Automated spec polish from `daily-regen` pre-flight.

**Spec:** `facet-grid`

## What changed
- **Data section**: Reformatted to explicit column schema with types and
size guidance (100–5000 points)
- **plot_type**: Removed redundant `grid` and `multi-panel` tags, kept
`facet` as the essential type
- **features**: Replaced non-canonical `subplots` and `conditioning`
with `faceted` (from canonical Layout features) and kept `comparison`

## Why
These changes improve clarity and consistency with the tagging
vocabulary defined in `spec-tags-generator.md`. The Data section now
follows the template format with explicit column definitions and
recommended data sizes.

## Hard guarantees from the prompt
- `id`, `issue`, `created` unchanged
- No semantic changes (data shape, plot type, requirements identical)
- `updated` bumped to current UTC

Auto-merge enabled — will merge once required checks pass.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: 3 people

plots/facet-grid/specification.md

@@ -13,19 +13,12 @@ A grid of subplots where each cell shows the same type of plot for a different s
 
 ## Data
 
-The visualization requires:
-- **Numeric variables**: For the base plot (x, y)
-- **Faceting variable(s)**: Categorical variables to split by (row, column)
-
-Example structure:
-```
-X    | Y    | Row_Var | Col_Var
------|------|---------|--------
-1.2  | 3.4  | A       | X
-2.3  | 4.5  | A       | Y
-3.1  | 2.8  | B       | X
-...
-```
+- `x` (numeric) - First axis variable for the base plot
+- `y` (numeric) - Second axis variable for the base plot
+- `row_facet` (categorical) - Variable to split rows
+- `col_facet` (categorical) - Variable to split columns
+- Size: 100–5000 points minimum (sufficient to show variation across facets)
+- Example: Palmer Penguins (split by species and island), or any dataset with 2+ categorical grouping variables
 
 ## Notes
 

plots/facet-grid/specification.yaml

@@ -1,11 +1,11 @@
 spec_id: facet-grid
 title: Faceted Grid Plot
 created: '2025-12-30T12:00:00Z'
-updated: '2025-12-30T12:00:00Z'
+updated: '2026-05-13T22:15:43Z'
 issue: 2696
 suggested: claude-code
 tags:
-  plot_type: [facet, grid, multi-panel]
+  plot_type: [facet]
   domain: [statistics, general]
-  features: [subplots, conditioning, comparison]
+  features: [faceted, comparison]
   data_type: [categorical, numeric]