Pass extra args through basectl test

[codeforester]

Summary

• Add basectl test <project> -- <args...> passthrough support for delegated test commands.
• Pass extra args through "$@" for normal test.command values and after mise run <task> -- for test.mise commands.
• Update README, command reference, architecture notes, and changelog.
• Add BATS coverage for command passthrough, dry-run quoting, mise passthrough, and --unknown after -- being treated as a test-runner arg.

Validation

HOME=/private/tmp/base-review-home bats cli/bash/commands/basectl/tests/basectl.bats
BASE_CACHE_DIR=/private/tmp/base-review-cache bin/basectl test base --dry-run -- -k focused
git diff --check

Not run: shellcheck --severity=error cli/bash/commands/basectl/subcommands/test.sh because shellcheck is not installed in this local environment.

Closes #255