feat(plotly): implement streamgraph-basic (#5699)

## Implementation: `streamgraph-basic` - python/plotly

Implements the **python/plotly** version of `streamgraph-basic`.

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

**Parent Issue:** #856

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25355962769)*

---------

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

Author: github-actions[bot]

plots/streamgraph-basic/implementations/python/plotly.py

@@ -1,103 +1,132 @@
-""" pyplots.ai
+""" anyplot.ai
 streamgraph-basic: Basic Stream Graph
-Library: plotly 6.5.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: plotly 6.7.0 | Python 3.13.13
+Quality: 88/100 | Updated: 2026-05-05
 """
 
+import sys
+
+
+sys.path.pop(0)
+
+import os
+
 import numpy as np
 import pandas as pd
 import plotly.graph_objects as go
 
 
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+GRID = "rgba(26,26,23,0.10)" if THEME == "light" else "rgba(240,239,232,0.10)"
+
+# Okabe-Ito palette — first series always #009E73
+OKABE_ITO = ["#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00", "#56B4E9"]
+
 # Data - Monthly streaming hours by music genre over 2 years
 np.random.seed(42)
 months = pd.date_range(start="2022-01-01", periods=24, freq="ME")
 genres = ["Pop", "Rock", "Hip-Hop", "Electronic", "Jazz", "Classical"]
 
-# Generate smooth, realistic streaming data
 base_values = {"Pop": 45, "Rock": 35, "Hip-Hop": 40, "Electronic": 25, "Jazz": 15, "Classical": 12}
 data = {}
 for genre in genres:
-    # Create smooth trends with seasonal variation
     trend = np.cumsum(np.random.randn(24) * 2)
     seasonal = 5 * np.sin(np.linspace(0, 4 * np.pi, 24))
     noise = np.random.randn(24) * 3
     values = base_values[genre] + trend + seasonal + noise
-    values = np.maximum(values, 5)  # Ensure positive values
+    values = np.maximum(values, 5)
     data[genre] = values
 
 df = pd.DataFrame(data, index=months)
+month_labels = months.strftime("%Y-%m").tolist()
 
 # Calculate streamgraph layout (centered baseline)
 values_array = df.values.T  # Shape: (n_genres, n_time_points)
 n_genres, n_time = values_array.shape
 
-# Calculate cumulative sums for stacking
 cumsum = np.vstack([np.zeros(n_time), np.cumsum(values_array, axis=0)])
-
-# Center the baseline symmetrically around the x-axis
 total = cumsum[-1]
 offset = total / 2
 
-# Colors - Python Blue and Yellow first, then colorblind-safe palette
-colors = ["#306998", "#FFD43B", "#E24A33", "#8EBA42", "#988ED5", "#348ABD"]
-
-# Create figure
+# Plot
 fig = go.Figure()
 
-# Add each genre as a filled area with smooth spline curves
 for i, genre in enumerate(genres):
     y_lower = cumsum[i] - offset
     y_upper = cumsum[i + 1] - offset
 
-    # Create coordinates for fill (forward then backward)
-    x_fill = list(months) + list(months)[::-1]
+    x_fill = month_labels + month_labels[::-1]
     y_fill = list(y_upper) + list(y_lower)[::-1]
 
+    # Dominant stream (Pop) at full opacity; others slightly dimmed for visual hierarchy
+    opacity = 1.0 if i == 0 else 0.80
+
     fig.add_trace(
         go.Scatter(
             x=x_fill,
             y=y_fill,
             fill="toself",
-            fillcolor=colors[i],
-            line={"color": colors[i], "width": 0.5, "shape": "spline", "smoothing": 1.0},
+            fillcolor=OKABE_ITO[i],
+            opacity=opacity,
+            line={"color": OKABE_ITO[i], "width": 0.5, "shape": "spline", "smoothing": 1.0},
             name=genre,
             mode="none",
             hoverinfo="name+x",
             hoveron="fills",
         )
     )
 
-# Update layout for 4800x2700 px
+subtitle = f"<span style='font-size:18px;color:{INK_SOFT}'>Monthly streaming hours by music genre, 2022–2023</span>"
+
 fig.update_layout(
-    title={"text": "streamgraph-basic · plotly · pyplots.ai", "font": {"size": 36}, "x": 0.5, "xanchor": "center"},
+    title={
+        "text": f"streamgraph-basic · plotly · anyplot.ai<br>{subtitle}",
+        "font": {"size": 28, "color": INK},
+        "x": 0.5,
+        "xanchor": "center",
+    },
     xaxis={
-        "title": {"text": "Month", "font": {"size": 28}},
-        "tickfont": {"size": 22},
-        "showgrid": True,
-        "gridcolor": "rgba(128,128,128,0.2)",
-        "gridwidth": 1,
+        "title": {"text": "Month", "font": {"size": 22, "color": INK}},
+        "tickfont": {"size": 18, "color": INK_SOFT},
+        "showgrid": False,
+        "showline": True,
+        "linecolor": INK_SOFT,
+        "mirror": False,  # bottom spine only — no top spine
+        "zeroline": False,
     },
     yaxis={
-        "title": {"text": "Streaming Hours (Millions)", "font": {"size": 28}},
-        "tickfont": {"size": 22},
+        "showticklabels": False,  # hide confusing negative offset values
         "showgrid": True,
-        "gridcolor": "rgba(128,128,128,0.2)",
+        "gridcolor": GRID,
         "gridwidth": 1,
         "zeroline": True,
-        "zerolinecolor": "rgba(128,128,128,0.3)",
+        "zerolinecolor": INK_SOFT,
         "zerolinewidth": 1,
+        "showline": False,  # no left spine (y labels hidden anyway)
+        "mirror": False,
+    },
+    legend={
+        "font": {"size": 18, "color": INK_SOFT},
+        "bgcolor": ELEVATED_BG,
+        "bordercolor": INK_SOFT,
+        "borderwidth": 1,
+        "orientation": "h",
+        "yanchor": "top",
+        "y": -0.12,
+        "xanchor": "center",
+        "x": 0.5,
     },
-    legend={"font": {"size": 22}, "orientation": "h", "yanchor": "bottom", "y": 1.02, "xanchor": "center", "x": 0.5},
-    template="plotly_white",
-    plot_bgcolor="white",
-    paper_bgcolor="white",
+    paper_bgcolor=PAGE_BG,
+    plot_bgcolor=PAGE_BG,
     hovermode="x unified",
-    margin={"l": 100, "r": 50, "t": 120, "b": 80},
+    margin={"l": 60, "r": 50, "t": 140, "b": 120},
 )
 
-# Save as PNG (4800x2700 px)
-fig.write_image("plot.png", width=1600, height=900, scale=3)
-
-# Save interactive HTML
-fig.write_html("plot.html", include_plotlyjs="cdn")
+# Save
+fig.write_image(f"plot-{THEME}.png", width=1600, height=900, scale=3)
+fig.write_html(f"plot-{THEME}.html", include_plotlyjs="cdn")