feat(seaborn): implement stem-basic (#5629)

## Implementation: `stem-basic` - python/seaborn

Implements the **python/seaborn** version of `stem-basic`.

**File:** `plots/stem-basic/implementations/python/seaborn.py`

**Parent Issue:** #972

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25171839176)*

---------

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/stem-basic/implementations/python/seaborn.py

@@ -1,48 +1,73 @@
-""" pyplots.ai
+""" anyplot.ai
 stem-basic: Basic Stem Plot
-Library: seaborn 0.13.2 | Python 3.13.11
-Quality: 91/100 | Created: 2025-12-23
+Library: seaborn 0.13.2 | Python 3.13.13
+Quality: 88/100 | Updated: 2026-04-30
 """
 
+import os
+
 import matplotlib.pyplot as plt
 import numpy as np
 import pandas as pd
 import seaborn as sns
 
 
+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"
+
+BRAND = "#009E73"
+
+sns.set_theme(
+    style="ticks",
+    rc={
+        "figure.facecolor": PAGE_BG,
+        "axes.facecolor": PAGE_BG,
+        "axes.edgecolor": INK_SOFT,
+        "axes.labelcolor": INK,
+        "text.color": INK,
+        "xtick.color": INK_SOFT,
+        "ytick.color": INK_SOFT,
+        "grid.color": INK,
+        "grid.alpha": 0.10,
+        "legend.facecolor": ELEVATED_BG,
+        "legend.edgecolor": INK_SOFT,
+    },
+)
+
 # Data - Discrete signal samples (damped sinusoidal impulse response)
 np.random.seed(42)
 n_samples = 30
 x = np.arange(n_samples)
 y = np.exp(-0.1 * x) * np.sin(0.5 * x) * 2.5
 
-# Create DataFrame for seaborn
 df = pd.DataFrame({"Sample Index": x, "Amplitude": y})
 
-# Plot
 fig, ax = plt.subplots(figsize=(16, 9))
 
 # Draw stems (thin vertical lines from baseline y=0 to data values)
-ax.vlines(x=df["Sample Index"], ymin=0, ymax=df["Amplitude"], color="#306998", linewidth=2.5, alpha=0.8)
+ax.vlines(x=df["Sample Index"], ymin=0, ymax=df["Amplitude"], color=BRAND, linewidth=2.5, alpha=0.8)
 
 # Draw markers at top of stems using seaborn
 sns.scatterplot(
-    data=df, x="Sample Index", y="Amplitude", s=300, color="#FFD43B", edgecolor="#306998", linewidth=2, ax=ax, zorder=3
+    data=df, x="Sample Index", y="Amplitude", s=300, color=BRAND, edgecolor=PAGE_BG, linewidth=2, ax=ax, zorder=3
 )
 
 # Draw baseline at y=0
-ax.axhline(y=0, color="#306998", linewidth=1.5, alpha=0.5)
+ax.axhline(y=0, color=INK_SOFT, linewidth=1.5, alpha=0.5)
 
-# Styling
 ax.set_xlabel("Sample Index (n)", fontsize=20)
 ax.set_ylabel("Amplitude", fontsize=20)
-ax.set_title("stem-basic · seaborn · pyplots.ai", fontsize=24)
+ax.set_title("stem-basic · seaborn · anyplot.ai", fontsize=24)
 ax.tick_params(axis="both", labelsize=16)
-ax.grid(True, alpha=0.3, linestyle="--")
 
-# Remove top and right spines for cleaner look
+ax.yaxis.grid(True, linestyle="-", linewidth=0.8, alpha=0.15)
+ax.set_axisbelow(True)
+
 ax.spines["top"].set_visible(False)
 ax.spines["right"].set_visible(False)
 
 plt.tight_layout()
-plt.savefig("plot.png", dpi=300, bbox_inches="tight")
+plt.savefig(f"plot-{THEME}.png", dpi=300, bbox_inches="tight", facecolor=PAGE_BG)