feat(highcharts): implement line-basic (#504)

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

**Parent Issue:** #205
**Sub-Issue:** #485
**Base Branch:** `plot/line-basic`
**Attempt:** 1/3

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

## Changes
- Basic line plot implementation using LineSeries
- Uses Python Blue color (#306998) from style guide
- Proper axis labels (Time, Value) and title
- Markers enabled on data points
- Targets 4800x2700px resolution
- PNG export via Selenium/headless Chrome

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

Author: claude[bot]

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

@@ -92,12 +92,16 @@
 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}")
 time.sleep(5)
-driver.save_screenshot("plot.png")
+
+# Capture the container element to get exact chart dimensions
+container = driver.find_element("id", "container")
+container.screenshot("plot.png")
+
 driver.quit()
 
 Path(temp_path).unlink()