feat(pygal): implement slope-basic (#9907)

## Implementation: `slope-basic` - python/pygal

Implements the **python/pygal** version of `slope-basic`.

**File:** `plots/slope-basic/implementations/python/pygal.py`

**Parent Issue:** #981

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/30179521392)*

---------

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/slope-basic/implementations/python/pygal.py

@@ -1,7 +1,7 @@
 """ anyplot.ai
 slope-basic: Basic Slope Chart (Slopegraph)
-Library: pygal 3.1.0 | Python 3.13.13
-Quality: 86/100 | Updated: 2026-04-30
+Library: pygal 3.1.3 | Python 3.13.14
+Quality: 85/100 | Updated: 2026-07-25
 """
 
 import os
@@ -21,10 +21,12 @@
 INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
 INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
 
-COLOR_INCREASE = "#009E73"  # Okabe-Ito position 1 — upward change
-COLOR_DECREASE = "#AE3030"  # imprint red — downward change
+COLOR_INCREASE = "#009E73"  # Imprint palette position 1 — upward change
+COLOR_DECREASE = "#AE3030"  # Imprint palette position 5 — semantic anchor for downward change
 
-# Realistic product category data — Q1 vs Q4 sales comparison
+# Realistic product category data — Q1 vs Q4 sales comparison.
+# Values are spread with even 7/8-unit gaps within each quarter so the
+# endpoint category-name labels never crowd or overlap each other.
 categories = [
     "Electronics",
     "Apparel",
@@ -37,8 +39,8 @@
     "Beauty",
     "Toys",
 ]
-q1_sales = [85, 72, 95, 45, 68, 52, 78, 62, 88, 40]
-q4_sales = [92, 58, 102, 75, 65, 71, 82, 48, 95, 55]
+q1_sales = [75, 82, 103, 40, 68, 47, 89, 61, 96, 54]
+q4_sales = [90, 58, 114, 74, 66, 82, 98, 42, 106, 50]
 
 increasing = [(c, q1_sales[i], q4_sales[i]) for i, c in enumerate(categories) if q4_sales[i] >= q1_sales[i]]
 decreasing = [(c, q1_sales[i], q4_sales[i]) for i, c in enumerate(categories) if q4_sales[i] < q1_sales[i]]
@@ -52,44 +54,48 @@
     foreground_strong=INK,
     foreground_subtle=INK_MUTED,
     colors=series_colors,
-    title_font_size=64,
-    label_font_size=44,
+    title_font_size=66,
+    label_font_size=56,
     major_label_font_size=44,
-    legend_font_size=38,
-    value_font_size=32,
-    value_label_font_size=36,
+    value_label_font_size=44,
+    # value_font_size drives pygal's dot-to-label offset (x/y = dot + value_font_size),
+    # not just the (unused, print_values=False) value text itself — raised well past
+    # the default 16 so category labels clear the y-axis line at the Q1 column.
+    value_font_size=40,
     stroke_width=6,
 )
 
-# Slope chart: Line chart with only 2 x-axis time points
+# Slope chart: Line chart with only 2 x-axis time points.
+# The legend is omitted — each line already carries its category name at
+# both endpoints (print_labels), and the up/down direction is self-evident
+# from the slope itself, so a color legend would only duplicate that info.
 chart = pygal.Line(
-    width=4800,
-    height=2700,
-    title="slope-basic · pygal · anyplot.ai",
+    width=3200,
+    height=1800,
+    title="slope-basic · python · pygal · anyplot.ai",
     x_title="Time Period",
-    y_title="Sales (units)",
+    y_title="Sales (thousands of units)",
     style=custom_style,
     show_dots=True,
     dots_size=18,
-    stroke_style={"width": 6},
     show_y_guides=True,
     show_x_guides=False,
-    show_legend=True,
+    show_legend=False,
     interpolate=None,
     margin=140,
     print_values=False,
     print_labels=True,
-    range=(30, 115),
-    margin_right=340,
+    range=(30, 120),
+    margin_right=480,
 )
 
 chart.x_labels = ["Q1 2024", "Q4 2024"]
 
-# Increasing categories — Okabe-Ito green
+# Increasing categories — Imprint brand green
 for c, start, end in increasing:
     chart.add(c, [{"value": start, "label": c}, {"value": end, "label": c}])
 
-# Decreasing categories — Okabe-Ito vermillion
+# Decreasing categories — Imprint matte red
 for c, start, end in decreasing:
     chart.add(c, [{"value": start, "label": c}, {"value": end, "label": c}])