feat: add bats-python-one-liner lint rule (#47)

[olavostauros]

Summary

Add a codebase lint rule that detects unreadable Python assertion one-liners (python3 -c "...assert...") in BATS test files, flagging them in favor of heredoc Python scripts for readability.

Fixes #47.

Detection

• Flags any .bats file line containing python3 -c or python -c where the inline code contains assert
• Skips @test description lines, full-line comments, heredoc context, and # codebase:ignore-annotated lines
• Supports file-level ignore via codebase:ignore bats-python-one-liner in mise.toml
• Outputs file:line citations with remediation hint

Files

File	Purpose
.mise/tasks/lint/bats-python-one-liner	Lint rule task
test/lint/bats-python-one-liner/bats-python-one-liner.bats	14 BATS tests
test/lint/bats-python-one-liner/fixtures/	9 fixture directories (clean, dirty-assert, dirty-python, dirty-long, heredoc, ignored-inline, ignored-file, empty)

Validation

• mise run test — all 232 tests pass (0 failures)
• codebase lint:bats-python-one-liner . — self-hosting passes clean (16 files, 0 violations)
• bash -n .mise/tasks/lint/bats-python-one-liner — syntax valid
• git diff --check