refactor(workspace): pass workspace object instead of id to service methods

- Replace workspace_id parameter with Workspace object reference in all workspace service methods
- Remove redundant find_workspace_by_id calls that were duplicated in each method
- Update all method signatures across approval, audit, billing, branding, core, settings and stats modules
- Modify SQL queries to bind ws.id instead of separate workspace_id parameter
- Add Workspace import to all affected modules
- Adjust method calls in API handlers to pass workspace object instead of id
- Consolidate workspace retrieval logic to single location per operation flow

models/workspaces/workspace.rs

@@ -3,7 +3,7 @@ use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, sqlx::FromRow)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, sqlx::FromRow, utoipa::ToSchema)]
 pub struct Workspace {
     pub id: Uuid,
     pub owner_id: Uuid,