feat: add admin account detail management

backend/app/schemas/admin.py

@@ -86,6 +86,15 @@ class AdminAccountUsageSummary(BaseModel):
     session_count_this_month: int = 0
 
 
+class AdminAccountInviteSummary(BaseModel):
+    id: UUID
+    email: EmailStr
+    role: str
+    expires_at: Optional[datetime] = None
+    created_at: datetime
+    used_at: Optional[datetime] = None
+
+
 class AdminAccountListItem(BaseModel):
     id: UUID
     name: str
@@ -110,6 +119,19 @@ class AdminAccountListResponse(BaseModel):
     per_page: int
 
 
+class AdminAccountDetailResponse(AdminAccountListItem):
+    invites: list[AdminAccountInviteSummary] = Field(default_factory=list)
+
+
+class AdminAccountCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=255)
+    plan: Literal["free", "pro", "team"] = "free"
+
+
+class AdminAccountUpdate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=255)
+
+
 # --- Audit Logs ---
 
 class AuditLogEntry(BaseModel):