Make VS Code installation truthful on aarch64

[CptPanko]

Fixes #297

Summary

• preserve presentation-command failures and show Done only after exit status 0
• install visual-studio-code-bin through the AUR helper on aarch64 while preserving the repository path elsewhere
• require the code command before changing VS Code configuration, applying the theme, or queuing a detached launch
• keep existing desktop-launch coverage aligned with the new executable postcondition

Verification

• bash test/shell.d/floating-terminal-test.sh
• bash test/shell.d/vscode-install-test.sh
• bash test/shell.d/desktop-entry-launch-test.sh
• bash test/shell.d/default-apps-test.sh
• bash test/shell.d/vscode-theme-test.sh
• /opt/homebrew/bin/bash bin/omarchy commands --check (454 commands)
• parser-aware syntax checks for all bin/omarchy-* commands
• Bash 3.2 syntax checks for touched shell files
• ShellCheck, git diff --check, conflict, secret, attribution, and author scans
• disposable mutations for wrapper status handling, the code postcondition, architecture routing, helper failure, and strict configuration failure

The full aggregate suite was bounded on macOS after three minutes in the existing sleep-lock test; focused affected tests pass. A real AUR install and VS Code runtime launch on Apple Silicon remain hardware-validation residuals.