Refactor shell scripts for improved safety and consistency; add guidelines to documentation

.github/copilot-instructions.md

@@ -133,6 +133,31 @@ This project is a financial transaction management application built with Astro
 
 ## Code Style & Conventions
 
+### Shell Scripts
+
+All shell scripts should follow these conventions:
+
+- Use `#!/usr/bin/env bash` instead of direct path to bash
+- Include standard safety flags at the start of each script:
+  ```bash
+  set -o errexit  # Exit on error
+  set -o errtrace # Exit on error inside functions
+  set -o nounset  # Error on undefined variables
+  set -o pipefail # Error if any command in a pipe fails
+  ```
+- Use `readonly` for constants and configuration values
+- Write error messages to stderr using `>&2`
+- Use proper error handling and exit codes
+- Validate all required parameters and dependencies
+- Use `[[` instead of `[` for better feature support
+- Quote all variable expansions
+- Use `${variable:-}` pattern for safe variable expansion
+- Handle special characters in input properly
+- Include clear error messages and validation
+- Group configuration/constants at the top of the script
+- Add descriptive comments for complex logic
+- Follow consistent indentation and formatting
+
 ### Import Path Aliases
 
 Always use the path aliases defined in `tsconfig.json` instead of relative imports. This makes the code more maintainable and easier to refactor.