[bug]: MPAndroidChart Displays "No chart data available

### Problem Description
The Stock Details screen fails to render the line graph for the stock's price history, showing a yellow label instead.

### Expected Solution
The MPAndroidChart should display a filled line graph of the daily/weekly price trend.

### Steps to Reproduce
1. Launch the app.
2. Click any stock from the Top Gainers list.
3. Observe the empty space below the header.

### Proposed Fix
Investigate `StockViewModel.kt` to ensure the API response is correctly mapping to MPAndroidChart `Entry(x, y)` objects. Ensure the `LineDataSet` is properly attached and `chart.invalidate()` is called on the main thread.

### Concerned Files
* `detailsFragment.kt`
* `StockViewModel.kt`
* `fragment_details.xml`

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### Acceptance Criteria
- [ ] Chart renders a line graph using the Alpha Vantage data.
- [ ] Chart scales correctly to fit the screen bounds.

Start by reproducing the empty chart from the Stock Details screen, then inspect detailsFragment.kt, StockViewModel.kt, and fragment_details.xml. Trace the Alpha Vantage response into MPAndroidChart Entry objects and the LineDataSet. Done means a filled daily/weekly line graph renders and scales within the screen bounds.

Written by the indexing model from the issue text.