feat(seaborn): implement spectrogram-basic (#2954)

## Implementation: `spectrogram-basic` - seaborn

Implements the **seaborn** version of `spectrogram-basic`.

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

**Parent Issue:** #2927

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20612803772)*

---------

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

Author: github-actions[bot]

plots/spectrogram-basic/implementations/seaborn.py

@@ -0,0 +1,76 @@
+""" pyplots.ai
+spectrogram-basic: Spectrogram Time-Frequency Heatmap
+Library: seaborn 0.13.2 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-31
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+import seaborn as sns
+from scipy import signal
+
+
+# Data - chirp signal with increasing frequency
+np.random.seed(42)
+sample_rate = 4000  # Hz
+duration = 2.0  # seconds
+t = np.linspace(0, duration, int(sample_rate * duration), endpoint=False)
+
+# Create a chirp signal: frequency increases from 100 Hz to 800 Hz
+f0, f1 = 100, 800
+chirp_signal = signal.chirp(t, f0=f0, f1=f1, t1=duration, method="linear")
+
+# Add some noise for realism
+chirp_signal += np.random.randn(len(chirp_signal)) * 0.1
+
+# Compute spectrogram using scipy
+nperseg = 256  # Window size
+noverlap = 200  # Overlap for smoother visualization
+frequencies, times, Sxx = signal.spectrogram(chirp_signal, fs=sample_rate, nperseg=nperseg, noverlap=noverlap)
+
+# Convert to dB scale for better visualization
+Sxx_dB = 10 * np.log10(Sxx + 1e-10)
+
+# Create plot
+fig, ax = plt.subplots(figsize=(16, 9))
+
+# Flip data vertically so low frequencies are at bottom (standard convention)
+Sxx_dB_flipped = np.flipud(Sxx_dB)
+
+# Use seaborn heatmap for the spectrogram visualization
+sns.heatmap(
+    Sxx_dB_flipped,
+    ax=ax,
+    cmap="viridis",
+    cbar=True,
+    cbar_kws={"label": "Power (dB)", "shrink": 0.8},
+    xticklabels=False,
+    yticklabels=False,
+    rasterized=True,
+)
+
+# Set proper axis labels and ticks
+# Calculate tick positions for time axis
+time_tick_positions = np.linspace(0, Sxx_dB.shape[1], 5)
+time_tick_labels = [f"{t:.1f}" for t in np.linspace(0, duration, 5)]
+ax.set_xticks(time_tick_positions)
+ax.set_xticklabels(time_tick_labels, fontsize=16)
+
+# Calculate tick positions for frequency axis (low to high, bottom to top)
+freq_tick_positions = np.linspace(0, Sxx_dB.shape[0], 5)
+freq_tick_labels = [f"{int(f)}" for f in np.linspace(frequencies[0], frequencies[-1], 5)]
+ax.set_yticks(freq_tick_positions)
+ax.set_yticklabels(freq_tick_labels[::-1], fontsize=16)
+
+# Labels and styling
+ax.set_xlabel("Time (s)", fontsize=20)
+ax.set_ylabel("Frequency (Hz)", fontsize=20)
+ax.set_title("spectrogram-basic · seaborn · pyplots.ai", fontsize=24, pad=20)
+
+# Adjust colorbar label size
+cbar = ax.collections[0].colorbar
+cbar.ax.tick_params(labelsize=14)
+cbar.ax.yaxis.label.set_size(18)
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight")

plots/spectrogram-basic/metadata/seaborn.yaml

@@ -0,0 +1,24 @@
+library: seaborn
+specification_id: spectrogram-basic
+created: '2025-12-31T05:34:16Z'
+updated: '2025-12-31T05:45:53Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20612803772
+issue: 2927
+python_version: 3.13.11
+library_version: 0.13.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/spectrogram-basic/seaborn/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/spectrogram-basic/seaborn/plot_thumb.png
+preview_html: null
+quality_score: 91
+review:
+  strengths:
+  - Excellent visualization of chirp signal showing clear time-frequency relationship
+    with bright diagonal trace
+  - Proper use of perceptually uniform viridis colormap as recommended in specification
+  - Well-formatted colorbar with dB units and appropriate sizing
+  - All text elements properly sized for the 16:9 aspect ratio output
+  - Correct use of seaborn heatmap for spectrogram visualization with proper axis
+    orientation
+  weaknesses:
+  - No grid lines present (minor issue for heatmap plots)