feat(seaborn): implement polar-line (#2700)

## Implementation: `polar-line` - seaborn

Implements the **seaborn** version of `polar-line`.

**File:** `plots/polar-line/implementations/seaborn.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20596056971)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/polar-line/implementations/seaborn.py

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+""" pyplots.ai
+polar-line: Polar Line Plot
+Library: seaborn 0.13.2 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+import seaborn as sns
+
+
+# Set seaborn style for consistent aesthetics
+sns.set_theme(style="whitegrid")
+
+# Data: Monthly average temperatures for two cities (cyclical pattern)
+np.random.seed(42)
+months = np.linspace(0, 2 * np.pi, 13)  # 12 months + closing point
+
+# City A: Temperate climate with moderate seasonal variation
+city_a_temps = np.array([5, 7, 12, 16, 20, 24, 26, 25, 21, 15, 9, 5, 5])
+
+# City B: More extreme seasonal variation
+city_b_temps = np.array([0, 2, 8, 14, 20, 26, 30, 29, 23, 14, 6, 1, 0])
+
+# Create polar plot
+fig, ax = plt.subplots(figsize=(12, 12), subplot_kw={"projection": "polar"})
+
+# Use seaborn color palette
+colors = sns.color_palette(["#306998", "#FFD43B"])
+
+# Plot lines using seaborn-styled matplotlib
+ax.plot(months, city_a_temps, color=colors[0], linewidth=3.5, marker="o", markersize=12, label="Coastal City")
+ax.plot(months, city_b_temps, color=colors[1], linewidth=3.5, marker="s", markersize=12, label="Inland City")
+
+# Fill area under curves with transparency
+ax.fill(months, city_a_temps, color=colors[0], alpha=0.15)
+ax.fill(months, city_b_temps, color=colors[1], alpha=0.15)
+
+# Set month labels
+month_labels = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+ax.set_xticks(np.linspace(0, 2 * np.pi, 12, endpoint=False))
+ax.set_xticklabels(month_labels, fontsize=18)
+
+# Style radial axis
+ax.set_ylim(0, 35)
+ax.set_yticks([0, 10, 20, 30])
+ax.set_yticklabels(["0°C", "10°C", "20°C", "30°C"], fontsize=14)
+
+# Title and legend
+ax.set_title("Monthly Temperature Patterns · polar-line · seaborn · pyplots.ai", fontsize=22, pad=30, fontweight="bold")
+ax.legend(loc="upper right", bbox_to_anchor=(1.15, 1.1), fontsize=16, frameon=True, fancybox=True)
+
+# Customize grid
+ax.grid(True, alpha=0.3, linestyle="--")
+ax.set_theta_zero_location("N")  # Start from top (January at 12 o'clock)
+ax.set_theta_direction(-1)  # Clockwise direction
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight", facecolor="white")

plots/polar-line/metadata/seaborn.yaml

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+library: seaborn
+specification_id: polar-line
+created: '2025-12-30T12:05:11Z'
+updated: '2025-12-30T12:09:42Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20596056971
+issue: 0
+python_version: 3.13.11
+library_version: 0.13.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/polar-line/seaborn/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/polar-line/seaborn/plot_thumb.png
+preview_html: null
+quality_score: 91
+review:
+  strengths:
+  - Excellent use of polar projection for cyclical monthly data
+  - Clear visual distinction between two temperature series with contrasting colors
+    and marker shapes
+  - Good use of filled areas to enhance visual comparison
+  - Proper clockwise month arrangement starting from January at top
+  - Clean, readable code structure following KISS principles
+  - Realistic and educational data scenario (coastal vs inland temperature patterns)
+  - Appropriate radial axis labels with temperature units
+  weaknesses:
+  - Does not use seaborn plotting functions (only styling utilities); implementation
+    relies entirely on matplotlib for actual plotting
+  - Legend placement causes overlap with title area