feat(letsplot): implement line-styled (#2641)

## Implementation: `line-styled` - letsplot

Implements the **letsplot** version of `line-styled`.

**File:** `plots/line-styled/implementations/letsplot.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20594564313)*

---------

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/line-styled/implementations/letsplot.py

@@ -0,0 +1,70 @@
+# ruff: noqa: F405
+"""pyplots.ai
+line-styled: Styled Line Plot
+Library: lets-plot | Python 3.13
+Quality: pending | Created: 2025-12-30
+"""
+
+import numpy as np
+import pandas as pd
+from lets_plot import *  # noqa: F403
+
+
+LetsPlot.setup_html()
+
+# Data - Monthly temperature readings from different weather stations
+np.random.seed(42)
+months = np.arange(1, 13)
+month_names = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+
+# Temperature patterns for different climate zones
+base_temp = np.array([2, 4, 8, 12, 17, 21, 24, 23, 19, 13, 7, 3])
+coastal = base_temp + np.random.randn(12) * 0.5 + 3
+continental = base_temp + np.random.randn(12) * 0.8 - 2
+mountain = base_temp + np.random.randn(12) * 0.6 - 8
+mediterranean = base_temp + np.random.randn(12) * 0.4 + 5
+
+# Create long-format DataFrame for lets-plot
+df = pd.DataFrame(
+    {
+        "Month": np.tile(months, 4),
+        "Month_Name": np.tile(month_names, 4),
+        "Temperature": np.concatenate([coastal, continental, mountain, mediterranean]),
+        "Station": np.repeat(["Coastal", "Continental", "Mountain", "Mediterranean"], 12),
+    }
+)
+
+# Create plot with different line styles
+plot = (
+    ggplot(df, aes(x="Month", y="Temperature", color="Station", linetype="Station"))
+    + geom_line(size=2.5)
+    + geom_point(size=5, alpha=0.8)
+    + scale_color_manual(values=["#306998", "#FFD43B", "#DC2626", "#22C55E"])
+    + scale_linetype_manual(values=["solid", "dashed", "dotted", "longdash"])
+    + scale_x_continuous(breaks=months.tolist(), labels=month_names)
+    + labs(
+        x="Month",
+        y="Temperature (°C)",
+        title="line-styled · letsplot · pyplots.ai",
+        color="Climate Zone",
+        linetype="Climate Zone",
+    )
+    + theme_minimal()
+    + theme(
+        plot_title=element_text(size=28, face="bold"),
+        axis_title=element_text(size=22),
+        axis_text=element_text(size=18),
+        legend_title=element_text(size=20),
+        legend_text=element_text(size=18),
+        legend_position="right",
+        panel_grid_major=element_line(color="#CCCCCC", size=0.5),
+        panel_grid_minor=element_line(color="#DDDDDD", size=0.3),
+    )
+    + ggsize(1600, 900)
+)
+
+# Save as PNG (scale 3x = 4800 × 2700 px)
+ggsave(plot, "plot.png", path=".", scale=3)
+
+# Save as HTML for interactive viewing
+ggsave(plot, "plot.html", path=".")

plots/line-styled/metadata/letsplot.yaml

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+library: letsplot
+specification_id: line-styled
+created: '2025-12-30T10:44:00Z'
+updated: '2025-12-30T10:56:50Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20594564313
+issue: 0
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-styled/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-styled/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-styled/letsplot/plot.html
+quality_score: 92
+review:
+  strengths:
+  - Excellent use of all four standard line styles (solid, dashed, dotted, longdash)
+    as specified
+  - Perfect title format following the {spec-id} · {library} · pyplots.ai convention
+  - 'Strong accessibility: combining color AND line style ensures print/colorblind
+    friendliness'
+  - Clean, readable code following KISS principles with proper seed for reproducibility
+  - Realistic climate zone temperature data that makes intuitive sense
+  - Well-sized text elements (28pt title, 22pt labels, 18pt ticks) appropriate for
+    4800×2700 output
+  weaknesses:
+  - Legend in code specifies color=Climate Zone and linetype=Climate Zone but the
+    data column is Station - while it works, the column naming is inconsistent
+  - All four climate zones follow the same basic seasonal pattern (low in winter,
+    high in summer) - could show more variation (e.g., Southern Hemisphere climate
+    with inverse pattern)