feat(altair): implement dumbbell-basic (#5419)

## Implementation: `dumbbell-basic` - python/altair

Implements the **python/altair** version of `dumbbell-basic`.

**File:** `plots/dumbbell-basic/implementations/python/altair.py`

**Parent Issue:** #945

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/24945139784)*

---------

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

Author: github-actions[bot]

plots/dumbbell-basic/implementations/python/altair.py

@@ -1,15 +1,27 @@
-""" pyplots.ai
+""" anyplot.ai
 dumbbell-basic: Basic Dumbbell Chart
-Library: altair 6.0.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: altair 6.1.0 | Python 3.14.4
+Quality: 89/100 | Updated: 2026-04-26
 """
 
+import os
+
 import altair as alt
 import pandas as pd
 
 
-# Data - Employee satisfaction scores before and after policy changes
-# Sorted by improvement (difference) to reveal patterns
+# Theme-adaptive chrome
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+
+# Okabe-Ito palette positions 1 and 2
+COLOR_BEFORE = "#009E73"
+COLOR_AFTER = "#D55E00"
+
+# Data — Employee satisfaction scores before and after policy changes
 data = pd.DataFrame(
     {
         "category": [
@@ -24,68 +36,72 @@
             "R&D",
             "IT",
         ],
-        "before": [52, 61, 58, 65, 72, 68, 55, 74, 63, 59],
-        "after": [78, 82, 76, 81, 85, 79, 64, 81, 69, 64],
+        "Before": [52, 61, 58, 65, 72, 68, 55, 74, 63, 59],
+        "After": [78, 82, 76, 81, 85, 79, 64, 81, 69, 64],
     }
 )
-
-# Calculate difference and sort by improvement
-data["difference"] = data["after"] - data["before"]
+data["difference"] = data["After"] - data["Before"]
 data = data.sort_values("difference", ascending=True)
 
-# Reshape data for Altair (long format for dots)
+# Long-form data for the two dot series
 dots_data = pd.melt(
-    data, id_vars=["category", "difference"], value_vars=["before", "after"], var_name="period", value_name="score"
+    data, id_vars=["category", "difference"], value_vars=["Before", "After"], var_name="period", value_name="score"
 )
 
-# Shared scale for x-axis
 x_scale = alt.Scale(domain=[45, 90])
+y_sort = alt.EncodingSortField(field="difference", order="ascending")
 
-# Create the connecting lines (using before/after as x values for line)
+# Connecting lines (theme-adaptive subtle ink)
 lines = (
     alt.Chart(data)
-    .mark_rule(strokeWidth=2, color="#999999")
-    .encode(
-        y=alt.Y(
-            "category:N",
-            sort=alt.EncodingSortField(field="difference", order="ascending"),
-            axis=alt.Axis(labelFontSize=18, titleFontSize=22, title=None),
-        ),
-        x=alt.X("before:Q", scale=x_scale),
-        x2=alt.X2("after:Q"),
-    )
+    .mark_rule(strokeWidth=3, color=INK_SOFT, opacity=0.55)
+    .encode(y=alt.Y("category:N", sort=y_sort, title=None), x=alt.X("Before:Q", scale=x_scale), x2=alt.X2("After:Q"))
 )
 
-# Create the dots with colors for before/after
+# Dots for Before / After values
 dots = (
     alt.Chart(dots_data)
-    .mark_circle(size=350)
+    .mark_circle(size=420, opacity=1.0, stroke=PAGE_BG, strokeWidth=2)
     .encode(
-        y=alt.Y("category:N", sort=alt.EncodingSortField(field="difference", order="ascending")),
-        x=alt.X(
-            "score:Q", axis=alt.Axis(labelFontSize=18, titleFontSize=22), title="Satisfaction Score", scale=x_scale
-        ),
+        y=alt.Y("category:N", sort=y_sort, title=None),
+        x=alt.X("score:Q", scale=x_scale, title="Employee Satisfaction Score (%)"),
         color=alt.Color(
             "period:N",
-            scale=alt.Scale(domain=["before", "after"], range=["#306998", "#FFD43B"]),
-            legend=alt.Legend(title="Period", labelFontSize=16, titleFontSize=18),
+            scale=alt.Scale(domain=["Before", "After"], range=[COLOR_BEFORE, COLOR_AFTER]),
+            legend=alt.Legend(title="Policy Change", labelFontSize=16, titleFontSize=18),
         ),
         tooltip=["category:N", "period:N", "score:Q"],
     )
 )
 
-# Combine lines and dots
 chart = (
     (lines + dots)
     .properties(
         width=1600,
         height=900,
-        title=alt.Title("Employee Satisfaction · dumbbell-basic · altair · pyplots.ai", fontSize=28),
+        title=alt.Title(
+            "Employee Satisfaction · dumbbell-basic · altair · anyplot.ai",
+            fontSize=28,
+            color=INK,
+            anchor="start",
+            offset=20,
+        ),
+        background=PAGE_BG,
+    )
+    .configure_view(fill=PAGE_BG, stroke=None)
+    .configure_axis(
+        labelFontSize=18,
+        titleFontSize=22,
+        domainColor=INK_SOFT,
+        tickColor=INK_SOFT,
+        gridColor=INK,
+        gridOpacity=0.10,
+        labelColor=INK_SOFT,
+        titleColor=INK,
     )
-    .configure_view(strokeWidth=0)
-    .configure_axis(grid=True, gridOpacity=0.3, gridDash=[4, 4])
+    .configure_title(color=INK)
+    .configure_legend(fillColor=ELEVATED_BG, strokeColor=INK_SOFT, labelColor=INK_SOFT, titleColor=INK, padding=12)
 )
 
-# Save as PNG and HTML
-chart.save("plot.png", scale_factor=3.0)
-chart.save("plot.html")
+chart.save(f"plot-{THEME}.png", scale_factor=3.0)
+chart.save(f"plot-{THEME}.html")