feat(matplotlib): implement line-markers (#2616)

## Implementation: `line-markers` - matplotlib

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

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

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20594555710)*

---------

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

Author: github-actions[bot]

plots/line-markers/implementations/matplotlib.py

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+""" pyplots.ai
+line-markers: Line Plot with Markers
+Library: matplotlib 3.10.8 | Python 3.13.11
+Quality: 94/100 | Created: 2025-12-30
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+
+# Data - Temperature readings over 14 days from weather stations
+np.random.seed(42)
+days = np.arange(1, 15)
+
+# Station A: Coastal location (moderate, stable)
+station_a = 18 + np.cumsum(np.random.randn(14) * 0.8)
+
+# Station B: Inland location (more variable)
+station_b = 15 + np.cumsum(np.random.randn(14) * 1.2)
+
+# Station C: Mountain location (cooler, different pattern)
+station_c = 10 + np.cumsum(np.random.randn(14) * 1.0)
+
+# Create plot
+fig, ax = plt.subplots(figsize=(16, 9))
+
+# Plot lines with different marker styles
+ax.plot(
+    days,
+    station_a,
+    marker="o",
+    markersize=12,
+    linewidth=3,
+    color="#306998",
+    label="Coastal Station",
+    markeredgecolor="white",
+    markeredgewidth=2,
+)
+
+ax.plot(
+    days,
+    station_b,
+    marker="s",
+    markersize=12,
+    linewidth=3,
+    color="#FFD43B",
+    label="Inland Station",
+    markeredgecolor="white",
+    markeredgewidth=2,
+)
+
+ax.plot(
+    days,
+    station_c,
+    marker="^",
+    markersize=12,
+    linewidth=3,
+    color="#E74C3C",
+    label="Mountain Station",
+    markeredgecolor="white",
+    markeredgewidth=2,
+)
+
+# Labels and styling
+ax.set_xlabel("Day", fontsize=20)
+ax.set_ylabel("Temperature (°C)", fontsize=20)
+ax.set_title("line-markers · matplotlib · pyplots.ai", fontsize=24)
+ax.tick_params(axis="both", labelsize=16)
+ax.grid(True, alpha=0.3, linestyle="--")
+ax.legend(fontsize=16, loc="best")
+
+# Set x-axis to show all days
+ax.set_xticks(days)
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight")

plots/line-markers/metadata/matplotlib.yaml

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+library: matplotlib
+specification_id: line-markers
+created: '2025-12-30T10:38:02Z'
+updated: '2025-12-30T10:45:06Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20594555710
+issue: 0
+python_version: 3.13.11
+library_version: 3.10.8
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-markers/matplotlib/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-markers/matplotlib/plot_thumb.png
+preview_html: null
+quality_score: 94
+review:
+  strengths:
+  - Excellent marker visibility with white edge borders creating strong contrast against
+    lines
+  - Three distinct marker shapes (circle, square, triangle) for easy series differentiation
+  - Realistic weather station scenario with plausible temperature ranges
+  - Clean, readable code following KISS principles
+  - Perfect title format and axis labels with units
+  weaknesses:
+  - Could demonstrate filled vs unfilled markers as suggested in spec notes for additional
+    distinction
+  - Legend placement inside plot area could potentially overlap with data in edge
+    cases
+  - Does not leverage more distinctive matplotlib features like annotations or custom
+    styling