Report missing project venv without a fatal trace

[codeforester]

Fixes #1884

What changed

• Report a missing project virtual environment through the normal error logger during activation.
• Preserve the nonzero exit status and uv-specific remediation.
• Add regression assertions that the expected missing-venv path emits no fatal marker or stack-trace header.

Root cause

Activation used the shared fatal helper for a user-actionable first-run prerequisite. That helper intentionally emits a Bash stack trace, making a missing uv environment look like an internal failure.

Validation

• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/activate.bats
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash bats cli/bash/commands/basectl/tests/project-command-helpers.bats
• BASE_BASH_LIBS_DIR=/Users/rameshhp/work/base-bash-libs/lib/bash ./bin/base-test (944 passed, 1 skipped; 852 BATS passed)
• Real missing-venv activation repro