Clear warning-level ShellCheck findings

[codeforester]

Summary

• clear warning-level ShellCheck findings across non-test Bash entrypoints, basectl command files, and shell snippets
• keep pass-by-name Bash 4.2 contracts explicit with focused ShellCheck directives
• replace the temporary PATH accumulator with a local variable and escape literal tilde cases without changing expansion behavior

Fixes #1493

Validation

• RED: bash -lc 'shellcheck -S warning base_init.sh bin/base-test bin/base-wrapper bin/basectl bootstrap.sh install.sh demo/demo.sh templates/project-install.sh cli/bash/commands/basectl/basectl.sh cli/bash/commands/basectl/subcommands/*.sh lib/bash/version/lib_version.sh lib/shell/*.sh lib/shell/bash_profile lib/shell/bashrc lib/shell/completions/basectl_completion.sh' failed with the existing SC2093, SC2034, SC2088, SC2229, SC2123, and SC2148 findings
• bash -lc 'shellcheck -S warning base_init.sh bin/base-test bin/base-wrapper bin/basectl bootstrap.sh install.sh demo/demo.sh templates/project-install.sh cli/bash/commands/basectl/basectl.sh cli/bash/commands/basectl/subcommands/*.sh lib/bash/version/lib_version.sh lib/shell/*.sh lib/shell/bash_profile lib/shell/bashrc lib/shell/completions/basectl_completion.sh'
• env BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats tests/install.bats tests/base_init.bats cli/bash/commands/basectl/tests/runtime-dispatch.bats cli/bash/commands/basectl/tests/runtime-shell.bats lib/bash/runtime/tests/runtime_bashrc.bats cli/bash/commands/basectl/tests/update-profile.bats cli/bash/commands/basectl/tests/gh.bats cli/bash/commands/basectl/tests/repo.bats cli/bash/commands/basectl/tests/export-context.bats cli/bash/commands/basectl/tests/onboard.bats
• bash -n base_init.sh bin/base-test bin/base-wrapper bin/basectl bootstrap.sh install.sh demo/demo.sh templates/project-install.sh cli/bash/commands/basectl/basectl.sh cli/bash/commands/basectl/subcommands/*.sh lib/bash/version/lib_version.sh lib/shell/*.sh lib/shell/bash_profile lib/shell/bashrc lib/shell/completions/basectl_completion.sh
• git diff --check
• env -u BASE_HOME BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash BASE_CACHE_DIR=/private/tmp/base-pr-train-1493 ./bin/base-test