Fix RSS filter buttons to update independently

[rajbos]

Closes #19

Implements independent updates for RSS filter buttons based on their exact text content.

• Adds a data-feed-name attribute to each filter button to store the exact feed name, ensuring that updates to button text are based on an exact match rather than using includes.
• Modifies the button text update logic to utilize the data-feed-name attribute for identifying the correct button to update, resolving the issue of incorrect updates when feed names share a common prefix.
• Updates the filterNews function to use the data-feed-name attribute for filtering news items, allowing for precise selection based on the feed name.

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