feat(plotnine): implement line-basic (#5538)

## Implementation: `line-basic` - python/plotnine

Implements the **python/plotnine** version of `line-basic`.

**File:** `plots/line-basic/implementations/python/plotnine.py`

**Parent Issue:** #653

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25117213621)*

---------

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/line-basic/implementations/python/plotnine.py

@@ -1,13 +1,39 @@
-""" pyplots.ai
+""" anyplot.ai
 line-basic: Basic Line Plot
-Library: plotnine 0.15.2 | Python 3.13.11
-Quality: 91/100 | Created: 2025-12-23
+Library: plotnine 0.15.3 | Python 3.13.13
+Quality: 89/100 | Updated: 2026-04-29
 """
 
+import os
+import sys
+
+
+# Prevent this file from shadowing the plotnine library when run from its own directory
+sys.path = [p for p in sys.path if not p or os.path.abspath(p) != os.path.abspath(os.path.dirname(__file__))]
+
 import numpy as np
 import pandas as pd
-from plotnine import aes, element_line, element_text, geom_line, geom_point, ggplot, labs, theme, theme_minimal
+from plotnine import (
+    aes,
+    element_line,
+    element_rect,
+    element_text,
+    geom_line,
+    geom_point,
+    ggplot,
+    labs,
+    scale_x_continuous,
+    theme,
+    theme_minimal,
+)
+
 
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+BRAND = "#009E73"
 
 # Data - Monthly average temperature readings for a typical year
 np.random.seed(42)
@@ -17,22 +43,27 @@
 
 df = pd.DataFrame({"Month": months, "Temperature": temperature})
 
+month_labels = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+
 # Plot
 plot = (
     ggplot(df, aes(x="Month", y="Temperature"))
-    + geom_line(size=2.5, color="#306998")
-    + geom_point(size=6, color="#306998")
-    + labs(x="Month", y="Temperature (°C)", title="line-basic · plotnine · pyplots.ai")
+    + geom_line(size=2.5, color=BRAND)
+    + geom_point(size=6, color=BRAND)
+    + scale_x_continuous(breaks=list(range(1, 13)), labels=month_labels)
+    + labs(x="Month", y="Temperature (°C)", title="line-basic · plotnine · anyplot.ai")
     + theme_minimal()
     + theme(
         figure_size=(16, 9),
-        text=element_text(size=14),
-        axis_title=element_text(size=20),
-        axis_text=element_text(size=16),
-        plot_title=element_text(size=24),
-        panel_grid_major=element_line(color="#cccccc", size=0.5, alpha=0.3),
-        panel_grid_minor=element_line(color="#eeeeee", size=0.3, alpha=0.2),
+        plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        panel_background=element_rect(fill=PAGE_BG),
+        text=element_text(size=14, color=INK),
+        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),
+        panel_grid_major=element_line(color=INK_SOFT, size=0.3, alpha=0.15),
+        panel_grid_minor=element_line(color=INK_SOFT, size=0.2, alpha=0.05),
     )
 )
 
-plot.save("plot.png", dpi=300, verbose=False)
+plot.save(f"plot-{THEME}.png", dpi=300, verbose=False)