Add Python test suite for note component parser library

[junior-ricon]

Problem

KnickKnackLabs/notes#127 adds the first explicit Python note-component parser surface (notes parse + lib/note_components.py). The PR kept BATS coverage for CLI behavior, but the library semantics are now substantial enough that they should eventually have a proper Python test suite.

During review, Or also caught that Python assertions embedded as single-line python3 -c commands in BATS are not acceptable. #127 fixed that locally by making the BATS assertions readable, and KnickKnackLabs/codebase#47 tracks a future lint for that smell. This issue tracks the more structural follow-up: test Python library semantics in Python.

Proposal

Add a small Python test suite for Python library code in notes, probably using pytest.

Suggested shape:

• Add pyproject.toml for Python test/dev dependencies.
• Add pytest as a dev/test dependency.
• Add a mise task such as test:python or integrate Python tests into the existing test task.
• Add tests under test/python/ or tests/ for:
  • parse_frontmatter_text;
  • parse_mapping_text;
  • parse_note_text / read_note_components;
  • malformed frontmatter remains body text;
  • comments/future conventions remain body text;
  • block-list parsing behavior already used by list/show/search.

BATS should remain the CLI/integration layer:

• notes parse <file> works through mise;
• NOTES_CALLER_PWD path resolution works;
• missing note exits nonzero;
• JSON is emitted.

Why not in #127

#127 is already the parser foundation PR and was intentionally narrowed several times: no notes read, no backmatter/banknotes, direct uv task, readable BATS assertions. Adding pytest in the same PR would widen scope. This is better as a follow-up once #127 lands.

Acceptance criteria

• Python parser/library behavior is covered by a Python test suite.
• Existing BATS parse tests are reduced to CLI integration checks where appropriate.
• The main mise run test path runs both BATS and Python tests, or the README clearly documents both test commands.
• No Python assertion one-liners remain in BATS for parser/library semantics.

Related

• Parser PR: KnickKnackLabs/notes#127
• Original read/query proposal: KnickKnackLabs/notes#126
• Future BATS lint: KnickKnackLabs/codebase#47
• Fold guidance: fold/notes/bats-tool-testing.md