chore(spec): auto-polish andrews-curves (#6817)

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

**Spec:** `andrews-curves`

## What changed
- Removed non-canonical `curve` tag from `plot_type` dimension (not in
canonical vocabulary per spec-tags-generator.md)
- Kept `line` as the appropriate canonical plot type (Andrews curves are
fundamentally line-based visualizations)
- Updated `updated` timestamp to current UTC

## Why
The `plot_type` dimension uses a canonical vocabulary where every tag
must be from the approved list (scatter, line, bar, pie, area, etc.).
The tag `curve` is not in the canonical table and violates this
constraint. The visualization is correctly characterized as `line`.

## 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/andrews-curves/specification.yaml

@@ -6,7 +6,7 @@ title: Andrews Curves for Multivariate Data
 
 # Specification tracking
 created: 2025-12-30T23:43:19Z
-updated: 2025-12-30T23:43:19Z
+updated: 2026-05-15T12:46:26Z
 issue: 2859
 suggested: MarkusNeusinger
 
@@ -15,7 +15,6 @@ suggested: MarkusNeusinger
 tags:
   plot_type:
     - line
-    - curve
   data_type:
     - numeric
     - multivariate