feat(letsplot): implement bar-diverging (#6034)

## Implementation: `bar-diverging` - python/letsplot

Implements the **python/letsplot** version of `bar-diverging`.

**File:** `plots/bar-diverging/implementations/python/letsplot.py`

**Parent Issue:** #2009

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25546837853)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/bar-diverging/implementations/python/letsplot.py

@@ -1,16 +1,29 @@
-""" pyplots.ai
+""" anyplot.ai
 bar-diverging: Diverging Bar Chart
-Library: letsplot 4.8.2 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-25
+Library: letsplot 4.9.0 | Python 3.13.13
+Quality: 93/100 | Updated: 2026-05-08
 """
 
+import os
+
 import pandas as pd
 from lets_plot import *  # noqa: F403
 from lets_plot.export import ggsave as export_ggsave
 
 
 LetsPlot.setup_html()  # noqa: F405
 
+# 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"
+
+# Okabe-Ito brand colors for diverging bars
+POSITIVE_COLOR = "#009E73"  # Brand green
+NEGATIVE_COLOR = "#D55E00"  # Vermillion
+
 # Data - Customer satisfaction survey (Net Promoter Score style)
 categories = [
     "Product Quality",
@@ -27,8 +40,8 @@
     "Loyalty Program",
 ]
 
-# Scores range from -100 (all detractors) to +100 (all promoters)
-scores = [72, 45, -28, 38, -12, 55, 21, 65, -35, 48, -8, 32]
+# More balanced scores: 6 negative, 6 positive
+scores = [62, 48, -22, 35, -15, 52, 28, 68, -38, 42, -8, 38]
 
 df = pd.DataFrame(
     {"Category": categories, "Score": scores, "Sentiment": ["Positive" if s >= 0 else "Negative" for s in scores]}
@@ -40,31 +53,44 @@
 # Preserve category order after sorting
 df["Category"] = pd.Categorical(df["Category"], categories=df["Category"].tolist(), ordered=True)
 
-# Create horizontal diverging bar chart
+# Create horizontal diverging bar chart with theme-adaptive styling
 plot = (
     ggplot(df, aes(x="Score", y="Category", fill="Sentiment"))  # noqa: F405
-    + geom_bar(stat="identity", width=0.7, alpha=0.9)  # noqa: F405
-    + geom_vline(xintercept=0, color="#333333", size=1.2)  # noqa: F405
-    + scale_fill_manual(values=["#DC2626", "#306998"])  # noqa: F405
+    + geom_bar(stat="identity", width=0.75, alpha=0.95)  # noqa: F405
+    + geom_vline(xintercept=0, color=INK_SOFT, size=1.5)  # noqa: F405
+    + scale_fill_manual(  # noqa: F405
+        values={
+            "Positive": POSITIVE_COLOR,
+            "Negative": NEGATIVE_COLOR,
+        }
+    )
     + labs(  # noqa: F405
-        x="Net Promoter Score", y="Category", title="bar-diverging · letsplot · pyplots.ai"
+        x="Net Promoter Score (-100 to +100)", y="Category", title="bar-diverging · letsplot · anyplot.ai"
     )
     + theme_minimal()  # noqa: F405
     + theme(  # noqa: F405
-        plot_title=element_text(size=28, face="bold", hjust=0.5),  # noqa: F405
-        axis_title_x=element_text(size=22),  # noqa: F405
-        axis_title_y=element_text(size=22),  # noqa: F405
-        axis_text_x=element_text(size=18),  # noqa: F405
-        axis_text_y=element_text(size=18),  # noqa: F405
-        legend_title=element_text(size=18),  # noqa: F405
-        legend_text=element_text(size=16),  # noqa: F405
-        legend_position="right",
+        plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),  # noqa: F405
+        panel_background=element_rect(fill=PAGE_BG),  # noqa: F405
+        panel_grid_major_x=element_line(color=INK, size=0.3),  # noqa: F405
         panel_grid_major_y=element_blank(),  # noqa: F405
         panel_grid_minor=element_blank(),  # noqa: F405
+        plot_title=element_text(size=28, face="bold", color=INK, hjust=0.5),  # noqa: F405
+        axis_title_x=element_text(size=22, color=INK),  # noqa: F405
+        axis_title_y=element_text(size=22, color=INK),  # noqa: F405
+        axis_text_x=element_text(size=18, color=INK_SOFT),  # noqa: F405
+        axis_text_y=element_text(size=18, color=INK_SOFT),  # noqa: F405
+        axis_line_x=element_line(color=INK_SOFT),  # noqa: F405
+        axis_line_y=element_line(color=INK_SOFT),  # noqa: F405
+        legend_title=element_text(size=18, color=INK),  # noqa: F405
+        legend_text=element_text(size=16, color=INK_SOFT),  # noqa: F405
+        legend_background=element_rect(fill=ELEVATED_BG, color=INK_SOFT),  # noqa: F405
+        legend_position="right",
     )
     + ggsize(1600, 900)  # noqa: F405
 )
 
-# Save
-export_ggsave(plot, filename="plot.png", path=".", scale=3)
-export_ggsave(plot, filename="plot.html", path=".")
+# Save PNG with scale 3x to get 4800 × 2700 px
+export_ggsave(plot, filename=f"plot-{THEME}.png", path=".", scale=3)
+
+# Save HTML for interactive version
+export_ggsave(plot, filename=f"plot-{THEME}.html", path=".")