feat(altair): implement scatter-annotated (#2817)

## Implementation: `scatter-annotated` - altair

Implements the **altair** version of `scatter-annotated`.

**File:** `plots/scatter-annotated/implementations/altair.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20602453376)*

---------

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plots/scatter-annotated/implementations/altair.py

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+""" pyplots.ai
+scatter-annotated: Annotated Scatter Plot with Text Labels
+Library: altair 6.0.0 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import altair as alt
+import numpy as np
+import pandas as pd
+
+
+# Data - Selected tech companies showing range of revenue/profit metrics
+np.random.seed(42)
+companies = ["NVIDIA", "Apple", "Microsoft", "Amazon", "Google", "Meta", "Adobe", "Oracle", "Tesla", "Intel"]
+# Revenue (billions USD) - realistic values
+revenue = np.array([61, 385, 211, 574, 307, 135, 19, 50, 97, 63])
+# Profit margin (%) - realistic values
+profit_margin = np.array([55, 25, 35, 6, 22, 20, 34, 26, 11, 8])
+
+df = pd.DataFrame({"company": companies, "revenue": revenue, "profit_margin": profit_margin})
+
+# Points layer
+points = (
+    alt.Chart(df)
+    .mark_point(size=250, filled=True, opacity=0.7, color="#306998")
+    .encode(
+        x=alt.X("revenue:Q", title="Revenue (Billions USD)", scale=alt.Scale(domain=[0, 620])),
+        y=alt.Y("profit_margin:Q", title="Profit Margin (%)", scale=alt.Scale(domain=[0, 60])),
+        tooltip=["company:N", "revenue:Q", "profit_margin:Q"],
+    )
+)
+
+# Text labels layer
+labels = (
+    alt.Chart(df)
+    .mark_text(align="left", dx=12, dy=-8, fontSize=18, fontWeight="bold", color="#333333")
+    .encode(x=alt.X("revenue:Q"), y=alt.Y("profit_margin:Q"), text="company:N")
+)
+
+# Combine layers
+chart = (
+    (points + labels)
+    .properties(
+        width=1600,
+        height=900,
+        title=alt.Title(text="scatter-annotated · altair · pyplots.ai", fontSize=28, anchor="middle"),
+    )
+    .configure_axis(labelFontSize=18, titleFontSize=22, gridOpacity=0.3)
+    .configure_view(strokeWidth=0)
+)
+
+# Save as PNG (4800x2700 with scale_factor=3)
+chart.save("plot.png", scale_factor=3.0)
+
+# Save as HTML for interactivity
+chart.save("plot.html")

plots/scatter-annotated/metadata/altair.yaml

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+library: altair
+specification_id: scatter-annotated
+created: '2025-12-30T17:49:20Z'
+updated: '2025-12-30T17:59:04Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20602453376
+issue: 0
+python_version: 3.13.11
+library_version: 6.0.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/scatter-annotated/altair/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/scatter-annotated/altair/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/scatter-annotated/altair/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent text legibility with appropriate font sizes for high-resolution output
+  - Clean declarative layer composition using Altair's grammar of graphics
+  - Realistic, neutral dataset with recognizable tech companies and accurate financials
+  - Smart label positioning with consistent dx/dy offsets to avoid point overlap
+  - Proper use of tooltips for interactivity in HTML output
+  weaknesses:
+  - Missing connector lines/arrows from labels to points as mentioned in specification
+    notes
+  - Could leverage more Altair-specific features like conditional formatting or selections