feat(letsplot): implement line-markers (#2630)

## Implementation: `line-markers` - letsplot

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

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

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20594559908)*

---------

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

Author: github-actions[bot]

plots/line-markers/implementations/letsplot.py

@@ -0,0 +1,54 @@
+""" pyplots.ai
+line-markers: Line Plot with Markers
+Library: letsplot 4.8.2 | Python 3.13.11
+Quality: 92/100 | Created: 2025-12-30
+"""
+
+import numpy as np
+import pandas as pd
+from lets_plot import *
+
+
+LetsPlot.setup_html()
+
+# Data - Quarterly product performance metrics
+np.random.seed(42)
+quarters = np.arange(1, 13)  # 12 quarters (3 years)
+
+# Three product lines with different growth patterns
+product_a = 45 + np.cumsum(np.random.randn(12) * 3) + np.arange(12) * 2
+product_b = 60 + np.cumsum(np.random.randn(12) * 4) + np.arange(12) * 1.5
+product_c = 35 + np.cumsum(np.random.randn(12) * 2.5) + np.arange(12) * 2.5
+
+df = pd.DataFrame(
+    {
+        "Quarter": list(quarters) * 3,
+        "Revenue": np.concatenate([product_a, product_b, product_c]),
+        "Product": ["Product A"] * 12 + ["Product B"] * 12 + ["Product C"] * 12,
+    }
+)
+
+# Create plot
+plot = (
+    ggplot(df, aes(x="Quarter", y="Revenue", color="Product"))
+    + geom_line(size=2.5)
+    + geom_point(size=6, alpha=0.9)
+    + scale_color_manual(values=["#306998", "#FFD43B", "#DC2626"])
+    + scale_x_continuous(breaks=list(range(1, 13)))
+    + labs(x="Quarter", y="Revenue (Million USD)", title="line-markers · lets-plot · pyplots.ai")
+    + theme_minimal()
+    + theme(
+        plot_title=element_text(size=28),
+        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),
+    )
+    + ggsize(1600, 900)
+)
+
+# Save outputs
+ggsave(plot, "plot.png", path=".", scale=3)
+ggsave(plot, "plot.html", path=".")

plots/line-markers/metadata/letsplot.yaml

@@ -0,0 +1,26 @@
+library: letsplot
+specification_id: line-markers
+created: '2025-12-30T10:39:36Z'
+updated: '2025-12-30T10:50:10Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20594559908
+issue: 0
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-markers/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-markers/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-markers/letsplot/plot.html
+quality_score: 92
+review:
+  strengths:
+  - Excellent text sizing for readability at target resolution (28pt title, 22pt axes,
+    18pt ticks)
+  - Clean ggplot2-style grammar with proper layering of geom_line and geom_point
+  - Realistic business scenario with quarterly product performance showing distinct
+    trends
+  - Good color contrast between the three product lines
+  - Markers are clearly visible against the lines with appropriate alpha (0.9)
+  weaknesses:
+  - Grid alpha 0.5 is too prominent - should be 0.2-0.4 for subtlety
+  - Could use different marker shapes for multiple series as suggested in the spec
+    notes