feat(letsplot): implement dumbbell-basic (#5421)

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

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

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

**Parent Issue:** #945

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/24945502773)*

---------

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

Author: github-actions[bot]

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

@@ -1,14 +1,18 @@
-""" pyplots.ai
+""" anyplot.ai
 dumbbell-basic: Basic Dumbbell Chart
-Library: letsplot 4.8.2 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: letsplot 4.9.0 | Python 3.14.4
+Quality: 86/100 | Updated: 2026-04-26
 """
 
+import os
+
 import pandas as pd
 from lets_plot import (
     LetsPlot,
     aes,
     element_blank,
+    element_line,
+    element_rect,
     element_text,
     geom_point,
     geom_segment,
@@ -26,7 +30,21 @@
 
 LetsPlot.setup_html()
 
-# Data - Employee satisfaction scores before and after policy changes
+# Theme tokens
+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"
+GRID = "#1A1A17" if THEME == "light" else "#F0EFE8"
+
+# Okabe-Ito palette — "After" comes first alphabetically → brand green
+BRAND = "#009E73"
+ACCENT = "#D55E00"
+SEGMENT = INK_SOFT
+
+# Data — Employee satisfaction scores before and after policy changes.
+# Mix of strong gains, modest shifts, and a regression to show full plot capability.
 categories = [
     "Engineering",
     "Marketing",
@@ -39,52 +57,54 @@
     "Legal",
     "R&D",
 ]
-before_scores = [62, 58, 71, 55, 68, 64, 59, 73, 66, 61]
-after_scores = [78, 72, 85, 74, 81, 76, 71, 88, 79, 75]
+before_scores = [62, 58, 71, 55, 68, 64, 72, 73, 66, 61]
+after_scores = [78, 72, 85, 80, 81, 70, 65, 88, 67, 75]
 
 df = pd.DataFrame({"category": categories, "before": before_scores, "after": after_scores})
-
-# Calculate difference for sorting - sort by improvement (largest first)
 df["diff"] = df["after"] - df["before"]
 df = df.sort_values("diff", ascending=True).reset_index(drop=True)
-
-# Create numeric y positions for categories (horizontal orientation)
 df["y_pos"] = range(len(df))
 
-# Create long-format data for points (to get legend)
 df_points = pd.concat(
     [
         pd.DataFrame({"y_pos": df["y_pos"], "value": df["before"], "period": "Before"}),
         pd.DataFrame({"y_pos": df["y_pos"], "value": df["after"], "period": "After"}),
     ]
 )
 
-# Plot - Horizontal dumbbell chart
+# Plot — horizontal dumbbell
 plot = (
     ggplot()
-    # Connecting lines - thin and subtle
-    + geom_segment(data=df, mapping=aes(x="before", xend="after", y="y_pos", yend="y_pos"), size=1.5, color="#888888")
-    # Points with color mapping for legend
+    + geom_segment(data=df, mapping=aes(x="before", xend="after", y="y_pos", yend="y_pos"), size=1.5, color=SEGMENT)
     + geom_point(data=df_points, mapping=aes(x="value", y="y_pos", color="period"), size=8)
-    + scale_color_manual(values=["#FFD43B", "#306998"], name="Period")
-    + labs(
-        x="Satisfaction Score", y="Department", title="Employee Satisfaction · dumbbell-basic · letsplot · pyplots.ai"
-    )
+    + scale_color_manual(values=[BRAND, ACCENT], name="Period")
     + scale_x_continuous(limits=[50, 95])
     + scale_y_continuous(breaks=list(range(len(df))), labels=df["category"].tolist())
+    + labs(
+        x="Satisfaction Score", y="Department", title="Employee Satisfaction · dumbbell-basic · letsplot · anyplot.ai"
+    )
     + ggsize(1600, 900)
     + theme_minimal()
     + theme(
-        axis_text_x=element_text(size=16),
-        axis_text_y=element_text(size=16),
-        axis_title=element_text(size=20),
-        plot_title=element_text(size=24, hjust=0.5),
-        legend_title=element_text(size=18),
-        legend_text=element_text(size=16),
+        plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        panel_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        legend_background=element_rect(fill=ELEVATED_BG, color=INK_SOFT),
+        panel_grid_major_x=element_line(color=GRID, size=0.3),
+        panel_grid_minor_x=element_line(color=GRID, size=0.2),
         panel_grid_major_y=element_blank(),
+        panel_grid_minor_y=element_blank(),
+        axis_line=element_line(color=INK_SOFT),
+        axis_ticks=element_blank(),
+        axis_title=element_text(size=20, color=INK),
+        axis_text=element_text(size=16, color=INK_SOFT),
+        plot_title=element_text(size=24, color=INK, hjust=0.5),
+        legend_title=element_text(size=18, color=INK),
+        legend_text=element_text(size=16, color=INK_SOFT),
+        legend_position=[0.88, 0.18],
+        legend_justification=[1, 0],
     )
 )
 
 # Save
-ggsave(plot, filename="plot.png", path=".", scale=3)
-ggsave(plot, filename="plot.html", path=".")
+ggsave(plot, filename=f"plot-{THEME}.png", path=".", scale=3)
+ggsave(plot, filename=f"plot-{THEME}.html", path=".")