This PR improves the https://modelcontextprotocol.io/clients page by adding the filter URL parameter, which automatically selects only the matching filters.

For example: https://modelcontextprotocol.io/clients?filter=Tools,Resources

Motivation and Context

This small change enables sharing/linking to a pre-filtered client list (e.g. from blog posts or docs) that highlights only the clients matching specific MCP features, and thus helps promote MCO clients that support the newer capabilities.

Here are the changes made:

• Read on mount: parse the filter query parameter, split by comma, and intersect with the known FEATURES whitelist before populating selectedFeatures. Unknown values are dropped, which is what makes this safe against HTML/script injection — combined with React's auto-escaping, no attacker-controlled string can reach the DOM.
• Write on change: a useEffect mirrors selectedFeatures back into the URL via history.replaceState, so toggling a filter updates the address bar in place (no new history entries, back button still works). Each feature name is encodeURIComponent-encoded individually; the , separator is left literal (it's a valid sub-delim per RFC 3986) so the URL reads as ?filter=Prompts,Tools,Discovery instead of ?filter=Prompts%2CTools%2CDiscovery.
• Both effects are SSR-safe (typeof window !== "undefined" guard).

How Has This Been Tested?

I've tested it locally in these scenarios:

• npm run serve:docs, open /clients?filter=Discovery,Resources — both filters auto-selected, list narrowed
• Open /clients?filter=Resources,BogusValue — only Resources selected (whitelist drops the unknown)
• Open /clients?filter=<script>alert(1)</script> — nothing selected, no script execution
• Click filter chips and confirm the URL updates in place; clicking "Clear filters" removes the param entirely

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context