feat(altair): implement ecdf-basic (#5357)

## Implementation: `ecdf-basic` - python/altair

Implements the **python/altair** version of `ecdf-basic`.

**File:** `plots/ecdf-basic/implementations/python/altair.py`

**Parent Issue:** #976

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/24890589158)*

---------

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

Author: github-actions[bot]

plots/ecdf-basic/implementations/python/altair.py

@@ -1,38 +1,72 @@
-""" pyplots.ai
+""" anyplot.ai
 ecdf-basic: Basic ECDF Plot
-Library: altair 6.0.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: altair 6.1.0 | Python 3.14.4
+Quality: 86/100 | Updated: 2026-04-24
 """
 
+import os
+
 import altair as alt
 import numpy as np
 import pandas as pd
 
 
-# Data
+# 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"
+BRAND = "#009E73"
+
+# Data: API response latency from a production web service
 np.random.seed(42)
-values = np.random.normal(loc=50, scale=15, size=200)
+response_times_ms = np.random.normal(loc=120, scale=35, size=250)
+response_times_ms = np.clip(response_times_ms, 20, None)
 
-# Sort values and compute ECDF
-sorted_values = np.sort(values)
-ecdf_y = np.arange(1, len(sorted_values) + 1) / len(sorted_values)
+sorted_latency = np.sort(response_times_ms)
+cumulative_proportion = np.arange(1, len(sorted_latency) + 1) / len(sorted_latency)
 
-df = pd.DataFrame({"value": sorted_values, "ecdf": ecdf_y})
+df = pd.DataFrame({"latency_ms": sorted_latency, "cumulative": cumulative_proportion})
 
 # Chart
 chart = (
     alt.Chart(df)
-    .mark_line(interpolate="step-after", strokeWidth=3, color="#306998")
+    .mark_line(interpolate="step-after", strokeWidth=3.5, color=BRAND)
     .encode(
-        x=alt.X("value:Q", title="Value", scale=alt.Scale(nice=True)),
-        y=alt.Y("ecdf:Q", title="Cumulative Proportion", scale=alt.Scale(domain=[0, 1])),
-        tooltip=["value:Q", "ecdf:Q"],
+        x=alt.X("latency_ms:Q", title="API Response Time (ms)", scale=alt.Scale(nice=True)),
+        y=alt.Y(
+            "cumulative:Q",
+            title="Cumulative Proportion",
+            scale=alt.Scale(domain=[0, 1]),
+            axis=alt.Axis(format=".0%", tickCount=11),
+        ),
+        tooltip=[
+            alt.Tooltip("latency_ms:Q", title="Latency (ms)", format=".1f"),
+            alt.Tooltip("cumulative:Q", title="Proportion", format=".3f"),
+        ],
+    )
+    .properties(
+        width=1600,
+        height=900,
+        background=PAGE_BG,
+        title=alt.Title("ecdf-basic · altair · anyplot.ai", fontSize=28, color=INK),
+    )
+    .interactive()
+    .configure_view(fill=PAGE_BG, strokeWidth=0)
+    .configure_axis(
+        domainColor=INK_SOFT,
+        tickColor=INK_SOFT,
+        gridColor=INK,
+        gridOpacity=0.10,
+        labelColor=INK_SOFT,
+        titleColor=INK,
+        labelFontSize=18,
+        titleFontSize=22,
     )
-    .properties(width=1600, height=900, title=alt.Title("ecdf-basic · altair · pyplots.ai", fontSize=28))
-    .configure_axis(labelFontSize=18, titleFontSize=22, gridOpacity=0.3, gridDash=[4, 4])
-    .configure_view(strokeWidth=0)
+    .configure_title(color=INK)
 )
 
 # Save
-chart.save("plot.png", scale_factor=3.0)
-chart.save("plot.html")
+chart.save(f"plot-{THEME}.png", scale_factor=3.0)
+chart.save(f"plot-{THEME}.html")