feat: add admin edit endpoint for server moderation (#315)

## Summary

Implements `PUT /v0/servers/{id}` admin edit endpoint to address part of
issue #182, providing an API-based solution for server moderation
without requiring direct database access.

- **New endpoint**: `PUT /v0/servers/{id}` for editing existing servers
- **Security**: Uses existing JWT auth with `PermissionActionEdit`
permissions
- **Anti-undelete protection**: Added `ServerStatusDeleted` status that
cannot be reverted
- **Full implementation**: Database, service, API, and comprehensive
test coverage

## Key Use Cases

- Mark malicious servers as `deleted` for takedown
- Update server metadata for moderation actions

Related to: https://github.com/modelcontextprotocol/registry/issues/182
(but that is not _done_ yet because we need admins to be able to login
(probably with #283), and need to add docs on how to do the takedown,
and probably guidelines on what we will/won't takedown)

internal/api/router/v0.go

@@ -17,6 +17,7 @@ func RegisterV0Routes(
 	v0.RegisterHealthEndpoint(api, cfg, metrics)
 	v0.RegisterPingEndpoint(api)
 	v0.RegisterServersEndpoints(api, registry)
+	v0.RegisterEditEndpoints(api, registry, cfg)
 	v0auth.RegisterAuthEndpoints(api, cfg)
 	v0.RegisterPublishEndpoint(api, registry, cfg)
 }