feat(vmcp): add support for ResourceLink content type

[Sanskarzz]

[WIP]

Summary

This PR implements support for the ResourceLink content type (type discriminant "resource_link") in the vMCP bridge layer. Previously, ResourceLink content returned by backend MCP servers was unrecognized by the conversion layer, causing it to fall through to "unknown" and eventually be emitted as empty text, losing critical resource pointers and metadata.

Key Changes

• Core Types: Extended vmcp.Content in pkg/vmcp/types.go to include Name and Description fields, allowing it to faithfully represent a ResourceLink .
• Conversion Layer: Added contentTypeLink constant to pkg/vmcp/conversion/content.go. Updated ConvertMCPContent to detect mcp.ResourceLink via type assertion and map it to vmcp.Content. Updated ToMCPContent to reconstruct mcp.ResourceLink using mcp.NewResourceLink.
• Tests: Added new test cases to TestConvertMCPContent and TestToMCPContent in conversion_test.go. Added TestResourceLinkRoundTrip to verify that data is preserved when converting in both directions.

Validation Results

All tests in pkg/vmcp/conversion and pkg/vmcp/server/adapter pass. go vet is clean.

Fixes #3960

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.57%. Comparing base (e42f226) to head (963b417).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4023      +/-   ##
==========================================
+ Coverage   68.53%   68.57%   +0.04%     
==========================================
  Files         441      441              
  Lines       44970    44979       +9     
==========================================
+ Hits        30820    30846      +26     
+ Misses      11758    11739      -19     
- Partials     2392     2394       +2     

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