Make subscription_type, username, and years optional on POST /v1/admin/users

- subscription_type defaults to lifetime when omitted; validated when provided
- years is only required (and enforced) when subscription_type is yearly
- username uniqueness check and validation are skipped when username is empty
- Update OpenAPI spec to reflect pubkey as the only required field

internal/http/docs/openapi.yaml

@@ -222,12 +222,12 @@ paths:
           application/json:
             schema:
               type: object
-              required: [pubkey, username, subscription_type]
+              required: [pubkey]
               properties:
                 pubkey: { type: string }
-                username: { type: string }
-                subscription_type: { type: string, enum: [yearly, lifetime] }
-                years: { type: integer }
+                username: { type: string, description: "Optional NIP-05 username to assign" }
+                subscription_type: { type: string, enum: [yearly, lifetime], description: "Defaults to lifetime when omitted" }
+                years: { type: integer, description: "Required when subscription_type is yearly" }
       responses:
         '201':
           description: Created

internal/http/handlers/admin_users.go

@@ -42,23 +42,29 @@ func (h *AdminUsers) Add(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	sub := user.SubscriptionType(body.SubscriptionType)
-	if !sub.Valid() {
+	if body.SubscriptionType == "" {
+		sub = user.SubLifetime
+	} else if !sub.Valid() {
 		WriteError(w, http.StatusBadRequest, "ValidationError", "invalid subscription_type")
 		return
 	}
+
 	years := body.Years
-	if years <= 0 {
-		years = 1
+	if sub == user.SubYearly && years <= 0 {
+		WriteError(w, http.StatusBadRequest, "ValidationError", "years is required for yearly subscription")
+		return
 	}
 
 	if existing, err := h.Users.Repo().GetByPubkey(r.Context(), hexpk); err == nil && existing != nil {
 		WriteError(w, http.StatusConflict, "Conflict", "user already exists")
 		return
 	}
+	if body.Username != "" {
 		if existing, err := h.Users.Repo().GetByUsername(r.Context(), user.NormalizeUsername(body.Username)); err == nil && existing != nil {
 			WriteError(w, http.StatusConflict, "Conflict", "username taken")
 			return
 		}
+	}
 
 	u, err := h.Users.CreateOrActivate(r.Context(), hexpk, body.Username, sub, years, true)
 	if err != nil {

internal/user/service.go

@@ -39,9 +39,11 @@ func (s *Service) IsAvailable(ctx context.Context, username string) (bool, error
 // concerns (e.g. payments worker uses this within a tx).
 func (s *Service) CreateOrActivate(ctx context.Context, pubkey, username string, sub SubscriptionType, years int, manual bool) (*User, error) {
 	username = NormalizeUsername(username)
+	if username != "" {
 		if err := ValidateUsername(username, s.reserved); err != nil {
 			return nil, err
 		}
+	}
 	now := time.Now().UTC()
 	expiresAt := computeExpiry(sub, years, time.Time{}, now)