spec: add bar-basic specification (#614)

## New Specification: `bar-basic`

Closes #612

---

### specification.md

# bar-basic: Basic Bar Chart

## Description

A vertical bar chart that displays categorical data with rectangular
bars whose heights are proportional to the values they represent. This
fundamental visualization is ideal for comparing discrete categories and
identifying which categories have the highest or lowest values. Bar
charts excel at showing rankings, distributions across categories, and
making relative comparisons intuitive.

## Applications

- Comparing quarterly sales figures across different product lines
- Visualizing survey responses showing preference counts for different
options
- Displaying population statistics across different age groups or
regions

## Data

- `category` (categorical) - Labels for each bar on the x-axis
- `value` (numeric) - Heights of the bars representing the measured
quantity
- Size: 3-15 categories recommended for readability
- Example: Product sales by category, survey response counts,
performance metrics by department

## Notes

- Bar widths should be consistent across all categories
- Consider adding value labels on or above bars for precise reading
- Use a single color for all bars, or highlight specific bars to draw
attention
- Ensure adequate spacing between bars for visual clarity

---

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---
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plots/bar-basic/specification.md

@@ -0,0 +1,25 @@
+# bar-basic: Basic Bar Chart
+
+## Description
+
+A vertical bar chart that displays categorical data with rectangular bars whose heights are proportional to the values they represent. This fundamental visualization is ideal for comparing discrete categories and identifying which categories have the highest or lowest values. Bar charts excel at showing rankings, distributions across categories, and making relative comparisons intuitive.
+
+## Applications
+
+- Comparing quarterly sales figures across different product lines
+- Visualizing survey responses showing preference counts for different options
+- Displaying population statistics across different age groups or regions
+
+## Data
+
+- `category` (categorical) - Labels for each bar on the x-axis
+- `value` (numeric) - Heights of the bars representing the measured quantity
+- Size: 3-15 categories recommended for readability
+- Example: Product sales by category, survey response counts, performance metrics by department
+
+## Notes
+
+- Bar widths should be consistent across all categories
+- Consider adding value labels on or above bars for precise reading
+- Use a single color for all bars, or highlight specific bars to draw attention
+- Ensure adequate spacing between bars for visual clarity

plots/bar-basic/specification.yaml

@@ -0,0 +1,29 @@
+# Specification-level metadata for bar-basic
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: bar-basic
+title: Basic Bar Chart
+
+# Specification tracking
+created: 2025-12-11T22:46:28Z
+issue: 612
+suggested: MarkusNeusinger
+history: []
+
+# Classification tags (applies to all library implementations)
+tags:
+  plot_type:
+    - bar
+  domain:
+    - general
+    - business
+    - statistics
+  features:
+    - basic
+    - comparison
+    - categorical
+  audience:
+    - beginner
+  data_type:
+    - categorical
+    - numeric