feat(invites): add bulk-create and soft-revoke invite endpoints

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/schemas/account.py

@@ -42,3 +42,12 @@ class AccountInviteResponse(BaseModel):
     used_at: Optional[datetime] = None
 
     model_config = {"from_attributes": True}
+
+
+class AccountInviteBulkCreate(BaseModel):
+    invites: list[AccountInviteCreate]
+
+
+class AccountInviteBulkResponse(BaseModel):
+    created: list[AccountInviteResponse]
+    failed: list[dict]  # entries shaped {"email": str, "error": str}