feat(plotly): implement spectrogram-basic (#2963)

## Implementation: `spectrogram-basic` - plotly

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

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

**Parent Issue:** #2927

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20612803590)*

---------

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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/plotly.py

@@ -0,0 +1,64 @@
+""" pyplots.ai
+spectrogram-basic: Spectrogram Time-Frequency Heatmap
+Library: plotly 6.5.0 | Python 3.13.11
+Quality: 93/100 | Created: 2025-12-31
+"""
+
+import numpy as np
+import plotly.graph_objects as go
+from scipy import signal
+
+
+# Data - Create a 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))
+
+# Chirp signal: frequency sweeps 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
+noise = np.random.randn(len(t)) * 0.1
+audio_signal = chirp_signal + noise
+
+# Compute spectrogram
+nperseg = 256  # Window size
+noverlap = 200  # Overlap for smooth visualization
+frequencies, times, Sxx = signal.spectrogram(audio_signal, fs=sample_rate, nperseg=nperseg, noverlap=noverlap)
+
+# Convert to dB scale for better visualization
+Sxx_db = 10 * np.log10(Sxx + 1e-10)
+
+# Create spectrogram heatmap
+fig = go.Figure()
+
+fig.add_trace(
+    go.Heatmap(
+        x=times,
+        y=frequencies,
+        z=Sxx_db,
+        colorscale="Viridis",
+        colorbar={
+            "title": {"text": "Power (dB)", "font": {"size": 20}},
+            "tickfont": {"size": 16},
+            "len": 0.85,
+            "thickness": 25,
+        },
+        hovertemplate="Time: %{x:.3f}s<br>Frequency: %{y:.0f}Hz<br>Power: %{z:.1f}dB<extra></extra>",
+    )
+)
+
+# Layout
+fig.update_layout(
+    title={"text": "spectrogram-basic · plotly · pyplots.ai", "font": {"size": 28}, "x": 0.5, "xanchor": "center"},
+    xaxis={"title": {"text": "Time (seconds)", "font": {"size": 22}}, "tickfont": {"size": 18}},
+    yaxis={"title": {"text": "Frequency (Hz)", "font": {"size": 22}}, "tickfont": {"size": 18}},
+    template="plotly_white",
+    margin={"l": 100, "r": 120, "t": 100, "b": 100},
+)
+
+# Save outputs
+fig.write_image("plot.png", width=1600, height=900, scale=3)
+fig.write_html("plot.html", include_plotlyjs="cdn")

plots/spectrogram-basic/metadata/plotly.yaml

@@ -0,0 +1,27 @@
+library: plotly
+specification_id: spectrogram-basic
+created: '2025-12-31T05:35:16Z'
+updated: '2025-12-31T05:47:16Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20612803590
+issue: 2927
+python_version: 3.13.11
+library_version: 6.5.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/spectrogram-basic/plotly/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/spectrogram-basic/plotly/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/spectrogram-basic/plotly/plot.html
+quality_score: 93
+review:
+  strengths:
+  - Excellent visual clarity with the Viridis colormap showing the chirp signal frequency
+    sweep distinctly
+  - Proper use of dB scale for power representation as recommended in spec
+  - Clean well-structured code following KISS principles
+  - Interactive hovertemplate provides detailed time/frequency/power information on
+    mouseover
+  - Correct title format and axis labeling with appropriate units
+  weaknesses:
+  - Missing grid lines (though acceptable for heatmap, subtle grid could help with
+    time/frequency reading)
+  - Could utilize more Plotly-specific interactive features like range sliders or
+    animation controls