Resolve setup projects from workspace

[codeforester]

Summary

• resolve basectl setup <project> through workspace project discovery when --manifest is not provided
• pass an explicit manifest to base_setup so setup does not accidentally use the current directory's nearest manifest
• keep base setup pinned to $BASE_HOME/base_manifest.yaml
• return Python setup-layer failures without dumping a Bash fatal stack trace
• update setup help notes and add BATS coverage for named project manifest resolution

Validation

• bash -n cli/bash/commands/basectl/subcommands/setup.sh
• bash -n cli/bash/commands/basectl/subcommands/setup_common.sh
• bats cli/bash/commands/basectl/tests/setup.bats
• bats cli/bash/commands/basectl/tests/basectl.bats
• env BASE_CACHE_DIR=/private/tmp/base-cache-test /Users/rameshhp/work/base/bin/basectl setup --dry-run --no-notify brew
• git diff --check