Install Arch dependencies using the existing package database and explain how to recover from stale package metadata. Avoid errexit on the first firmware count, handle Secure Boot prompt EOF as cancellation, propagate error traps into functions, and reject empty firmware sources before modifying installed firmware.
Validation: eight isolated installer regression tests pass; the original installer fails the affected cases. Bash syntax and ShellCheck error-level checks pass. Fixes#100. Addresses the confirmed findings in #108; other audit suggestions remain separate.
