Add tool definitions annotation support to registry server

[lujunsan]

Adds support for the toolhive.stacklok.dev/tool-definitions annotation to the registry server, allowing MCP server publishers to declare custom tool definitions that are exposed through the registry API.

This implements the registry-server side of RFC-0015.

Changes

• Added defaultRegistryToolDefinitionsAnnotation constant for the tool definitions annotation
• Created shared extractToolDefinitions() helper function to parse and validate tool definitions
• Updated all three resource extraction functions to support tool definitions:
  • extractServer() (MCPServer)
  • extractVirtualMCPServer() (VirtualMCPServer)
  • extractMCPRemoteProxy() (MCPRemoteProxy)
• Tool definitions are parsed as JSON to validate syntax, but schema validation is not performed (operator's responsibility)
• Parsed tool definitions are stored in _meta.publisher-provided.<url>.tool_definitions
• Added comprehensive unit tests for all three resource types covering valid, invalid, empty, and multiple tool scenarios

Technical Details

The registry server reads the toolhive.stacklok.dev/tool-definitions annotation from Kubernetes MCP resources and:

1. Validates the annotation contains valid JSON syntax
2. Logs a warning and skips if JSON is invalid
3. Stores the parsed structure in the server metadata for API exposure
4. Maintains backward compatibility - resources without tool definitions continue to work

The implementation does NOT validate the tool definition schema itself, as that is the operator's responsibility during reconciliation.

Testing

• Manual testing performed with test Kubernetes resources
• Unit tests added following existing table-driven test patterns
• Verified tool definitions appear correctly in API responses as JSON arrays
• Tested backward compatibility with resources lacking tool definitions

Related

• Implements RFC-0015 (registry-server side)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.17%. Comparing base (5b09174) to head (8bc8904).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #414      +/-   ##
==========================================
+ Coverage   61.08%   61.17%   +0.09%     
==========================================
  Files          81       81              
  Lines        7426     7444      +18     
==========================================
+ Hits         4536     4554      +18     
  Misses       2582     2582              
  Partials      308      308              

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