feat(altair): implement line-basic (#1352)

## Implementation: `line-basic` - altair

Implements the **altair** version of `line-basic`.

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

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20447578895)*

---------

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

Author: github-actions[bot]

plots/line-basic/implementations/altair.py

@@ -1,7 +1,7 @@
 """ pyplots.ai
 line-basic: Basic Line Plot
 Library: altair 6.0.0 | Python 3.13.11
-Quality: 93/100 | Created: 2025-12-13
+Quality: 91/100 | Created: 2025-12-23
 """
 
 import altair as alt
@@ -32,7 +32,7 @@
 # Add points to enhance visibility
 points = alt.Chart(df).mark_point(size=200, color="#306998", filled=True).encode(x="Month:T", y="Temperature:Q")
 
-# Combine line and points
+# Combine line and points with subtle grid
 final_chart = (chart + points).configure_axis(gridColor="#E0E0E0", gridOpacity=0.3).configure_view(strokeWidth=0)
 
 # Save

plots/line-basic/metadata/altair.yaml

@@ -1,17 +1,25 @@
 library: altair
 specification_id: line-basic
-created: 2025-12-13 23:40:11+00:00
-updated: 2025-12-13 23:40:11+00:00
+created: '2025-12-23T00:24:33Z'
+updated: '2025-12-23T00:28:20Z'
 generated_by: claude-opus-4-5-20251101
-workflow_run: 20199516689
-issue: 653
+workflow_run: 20447578895
+issue: 0
 python_version: 3.13.11
 library_version: 6.0.0
 preview_url: https://storage.googleapis.com/pyplots-images/plots/line-basic/altair/plot.png
 preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-basic/altair/plot_thumb.png
 preview_html: https://storage.googleapis.com/pyplots-images/plots/line-basic/altair/plot.html
-quality_score: 93
+quality_score: 91
 review:
-  strengths: []
-  weaknesses: []
-  improvements: []
+  strengths:
+  - Excellent visual clarity with properly sized text elements and line/point visibility
+  - Perfect spec compliance with correct title format and all required features
+  - Realistic, comprehensible data scenario (monthly temperature with seasonal pattern)
+  - Clean KISS code structure following project guidelines
+  - Good use of layered chart (line + points) for enhanced visibility
+  - Proper temporal encoding (:T) for datetime data
+  weaknesses:
+  - Missing Altair distinctive interactive features (tooltips, .interactive() for
+    zoom/pan) that showcase the library strengths
+  - Grid lines are too subtle (gridOpacity=0.3) making them barely visible