Add search term to URL fragment for shareable search links

[Copilot]

This PR adds the ability to share URLs with search filters applied. When a user searches for models in the pricing table, the search term is now automatically saved to the URL fragment, making it easy to share links with specific model filters.

Changes

The search term is stored using a short URL parameter q to keep URLs concise. For example, searching for "claude" results in a URL like https://llm-prices.com/#q=claude.

Implementation Details

• URL Persistence: The search term is saved to and restored from the URL hash parameter q
• Seamless Integration: Works alongside existing URL parameters for tokens, costs, sorting, and model selection
• Automatic Cleanup: The q parameter is automatically removed from the URL when the search box is cleared
• URL Encoding: Properly handles multi-word searches (e.g., "gpt mini" becomes #q=gpt+mini)

Example Usage

Users can now:

1. Search for specific models (e.g., "claude", "gpt mini", "gemini flash")
2. Share the URL with the search filter preserved
3. Reload the page or send the link to others, and the search will be automatically restored

Screenshot

The screenshot shows the search box with "claude" entered, the filtered table showing only Claude models, and the URL containing #q=claude.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update fragment URL with current search filter term</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #19

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