Add D3.js line chart for views over time on metrics page

[lukepayyapilli]

Summary

• Added a D3.js line chart displayed side-by-side with the unique registered project views card on the metrics page.
• Used D3 v3 and d3-tip (already bundled) with inline styles matching the existing charts.html pattern.
• Chart data serialized via a _format_chart_data helper to keep the view focused on data retrieval.
• Included fixtures, integration tests, and unit tests for the chart data.

Approach

The project already bundles D3 v3 and d3-tip for the site-wide statistics charts. Rather than introducing a new charting library, we reuse the same dependencies and follow the same pattern established in search/templates/search/charts.html.

Chart data is prepared in the view via a small _format_chart_data helper that serializes the chronological views-over-time data as JSON. This keeps the view as the presenter (gathering and shaping data for the template) while extracting the formatting detail into a named function. The template receives the JSON and renders it inline — no additional REST endpoint needed since the dataset is small (max ~100 months).

The chart is displayed in chronological order (oldest to newest) alongside the counts card, while the table below remains reverse-chronological (newest first) with pagination. Each format follows its natural convention.

Screenshot

Normal View:

Long History:

Short History:

No History:

Closes #2562