fix: resolve compilation errors and update SQLx to 0.7

[maheshbhatiya73]

Fix multiple compilation issues in Rust backend:

• Add serde feature to uuid dependency for proper serialization
• Fix SQLx imports and API compatibility for version 0.7
• Convert query macros to regular queries to avoid compile-time DB requirement
• Fix borrowing issues in update_plugin function
• Create AppState struct to resolve router state type mismatch
• Clean up unused imports across modules
• Update PgPoolOptions usage to match SQLx 0.7 API

The backend should now compile and run successfully without requiring a database connection at compile time or cargo sqlx prepare.