feat(highcharts): implement line-basic (#448)

## Summary
Implements `line-basic` for **highcharts** library.

**Parent Issue:** #205
**Sub-Issue:** #438
**Base Branch:** `plot/line-basic`
**Attempt:** 1/3

## Implementation
- `plots/highcharts/line/line-basic/default.py`

## Features
- Basic line plot with data points connected by lines
- Uses Python Blue color (#306998) from style guide
- Proper axis labels (Time on X-axis, Value on Y-axis)
- Title "Basic Line Plot"
- Markers enabled on data points
- Follows 4800x2700 px image dimensions requirement

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

Author: claude[bot]

plots/highcharts/line/line-basic/default.py

@@ -40,10 +40,13 @@
     "title": {"text": "Time", "style": {"fontSize": "40px"}},
     "categories": time_values,
     "labels": {"style": {"fontSize": "32px"}},
+    "lineWidth": 2,
+    "tickWidth": 2,
 }
 chart.options.y_axis = {
     "title": {"text": "Value", "style": {"fontSize": "40px"}},
     "labels": {"style": {"fontSize": "32px"}},
+    "gridLineWidth": 1,
     "gridLineColor": "#e0e0e0",
 }
 
@@ -89,7 +92,7 @@
 chrome_options.add_argument("--no-sandbox")
 chrome_options.add_argument("--disable-dev-shm-usage")
 chrome_options.add_argument("--disable-gpu")
-chrome_options.add_argument("--window-size=4800,2700")
+chrome_options.add_argument("--window-size=4900,2800")
 
 driver = webdriver.Chrome(options=chrome_options)
 driver.get(f"file://{temp_path}")