Remove requirement of repository.id from server.json (#285)

Make repository.id optional by:
- Removing 'id' from required fields in JSON schema
- Adding omitempty tags to Go model structs 
- Updating examples to show simpler format without id

This fixes publishing failures where the publisher tool doesn't 
generate repository.id but the schema requires it.

Fixes #179

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Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: adam jones <domdomegg@users.noreply.github.com>

internal/model/model.go

@@ -31,7 +31,7 @@ type PublishRequest struct {
 type Repository struct {
 	URL    string `json:"url" bson:"url"`
 	Source string `json:"source" bson:"source"`
-	ID     string `json:"id" bson:"id"`
+	ID     string `json:"id,omitempty" bson:"id,omitempty"`
 }
 
 // ServerList represents the response for listing servers as defined in the spec