Add default setup notifications

[codeforester]

Summary

• make basectl setup send best-effort macOS completion/failure notifications by default
• skip notifications during --dry-run
• add basectl setup --no-notify and BASE_SETUP_NOTIFY=false as opt-outs
• resolve named setup projects through workspace discovery before invoking base_setup
• pass an explicit manifest to base_setup so basectl setup <project> does not accidentally use the current directory's nearest manifest
• return Python setup-layer failures without dumping a Bash fatal stack trace
• document the notification behavior and remove the completed TODO item
• add BATS coverage for default success, default failure, dry-run skip, CLI opt-out, env opt-out, help text, and 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