feat(altair): implement slider-control-basic (#3101)

## Implementation: `slider-control-basic` - altair

Implements the **altair** version of `slider-control-basic`.

**File:** `plots/slider-control-basic/implementations/altair.py`

**Parent Issue:** #3071

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20620344480)*

---------

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

Author: github-actions[bot]

plots/slider-control-basic/implementations/altair.py

@@ -0,0 +1,73 @@
+""" pyplots.ai
+slider-control-basic: Interactive Plot with Slider Control
+Library: altair 6.0.0 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-31
+"""
+
+import altair as alt
+import numpy as np
+import pandas as pd
+
+
+# Data - Monthly sales data across multiple years
+np.random.seed(42)
+years = [2019, 2020, 2021, 2022, 2023]
+months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+
+data = []
+base_sales = 100
+for year in years:
+    # Different growth patterns per year
+    year_factor = 1 + (year - 2019) * 0.15
+    for i, month in enumerate(months):
+        # Seasonal pattern with noise
+        seasonal = np.sin(i * np.pi / 6) * 20 + 10
+        sales = base_sales * year_factor + seasonal + np.random.normal(0, 10)
+        data.append({"Year": year, "Month": month, "Month_Num": i + 1, "Sales": max(0, sales)})
+
+df = pd.DataFrame(data)
+
+# Create slider binding for year selection
+year_slider = alt.binding_range(min=2019, max=2023, step=1, name="Year: ")
+year_selection = alt.selection_point(fields=["Year"], bind=year_slider, value=2023)
+
+# Bar chart showing monthly sales for selected year
+chart = (
+    alt.Chart(df)
+    .mark_bar(size=40, color="#306998", opacity=0.8)
+    .encode(
+        x=alt.X("Month:N", sort=months, axis=alt.Axis(labelFontSize=18, titleFontSize=22, labelAngle=0), title="Month"),
+        y=alt.Y(
+            "Sales:Q",
+            axis=alt.Axis(labelFontSize=18, titleFontSize=22),
+            title="Sales (thousands $)",
+            scale=alt.Scale(domain=[0, 200]),
+        ),
+        tooltip=[
+            alt.Tooltip("Year:O", title="Year"),
+            alt.Tooltip("Month:N", title="Month"),
+            alt.Tooltip("Sales:Q", title="Sales", format=".1f"),
+        ],
+    )
+    .add_params(year_selection)
+    .transform_filter(year_selection)
+    .properties(
+        width=1600,
+        height=900,
+        title=alt.Title(
+            "slider-control-basic · altair · pyplots.ai",
+            fontSize=28,
+            anchor="middle",
+            subtitle="Use the Year slider to filter monthly sales data",
+            subtitleFontSize=18,
+        ),
+    )
+    .configure_axis(gridColor="#cccccc", gridOpacity=0.3, domainColor="#333333")
+    .configure_view(strokeWidth=0)
+)
+
+# Save as PNG (static snapshot at default year)
+chart.save("plot.png", scale_factor=3.0)
+
+# Save as HTML (interactive version with working slider)
+chart.save("plot.html")

plots/slider-control-basic/metadata/altair.yaml

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+library: altair
+specification_id: slider-control-basic
+created: '2025-12-31T13:54:14Z'
+updated: '2025-12-31T14:05:06Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20620344480
+issue: 3071
+python_version: 3.13.11
+library_version: 6.0.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/slider-control-basic/altair/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/slider-control-basic/altair/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/slider-control-basic/altair/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent use of Altair declarative selection and binding system for the slider
+  - Clean readable code following KISS principles
+  - Realistic business scenario with seasonal sales patterns
+  - Good visual design with appropriate font sizes and color choice
+  - Both PNG and HTML outputs provided for static and interactive use
+  weaknesses:
+  - Y-axis scale starts at 0 but data ranges from 140-190 creating unused space at
+    bottom
+  - Current slider value not prominently displayed near the slider as spec suggests