Align local lint/format gates with CI-covered paths

[lbliii]

Context

Local make lint and CI lint do not cover the same paths. That creates avoidable CI-only failures and makes the local done criteria less trustworthy.

Evidence

• Makefile local lint runs uv run ruff check src/ tests/.
• Makefile local format-check runs uv run ruff format --check src/ tests/.
• .github/workflows/tests.yml lint job runs uv run ruff check src/kida tests/ benchmarks/ scripts/ and uv run ruff format --check src/kida tests/ benchmarks/ scripts/.
• pyproject.toml has per-file ignores for benchmarks/**/*.py, examples/**/*.py, and scripts/**/*.py, but local gates do not use all of those scoped ignores.

Proposed Scope

• Decide the authoritative lint/format path set.
• Update Makefile and CI to match.
• Consider adding examples/ if examples are treated as copied production code.

Done When

• Running local lint/format is predictive of CI lint/format.
• The path set is documented in docs/stability-gate.md or Makefile help.
• Any intentionally excluded path has a reason.