feat: add Webhound MCP server

[mfkhalil]

Summary

• add Webhound as a remote Streamable HTTP MCP server
• configure per-user OAuth with dynamic client registration and PKCE; no API key, bearer token, client secret, or shared publisher credential is included
• list the complete 30-tool surface and document the dollar-budget research contract, terminal done=true rule, reports, datasets, and evidence packs

Testing

• official catalog validator: all 111 entries valid
• official catalog build passed
• catalog Go test suite passed
• current ToolHive OAuth / DCR / PKCE source tests passed
• the same production endpoint completed a live DCR / PKCE account flow in Goose, discovered all 30 tools, and called webhound_account without starting research or spending credits

I did not claim a native ToolHive runtime smoke: Docker was initially stopped, and starting it automatically resumed nine unrelated pre-existing containers. I created no ToolHive workload, touched no container, and returned Docker Desktop to its prior stopped state rather than risking user workloads.