Replace direct $1/$2/$3 usage with named local variables in _log(),
msg(), msg_err(), msg_done(), msg_run(), msg_ok(), and array_diff()
(SonarCloud rule shelldre:S7679).
Add return 0 as the last statement in ~46 shell functions across
17 files that previously relied on implicit return codes
(SonarCloud rule shelldre:S7682).
Replace single brackets with double brackets in bash conditional
expressions across 14 files (28 changes). All scripts use bash
shebangs so [[ is safe everywhere (SonarCloud rule shelldre:S7688).
