[P1] Enforce cross-platform line-ending and format-check parity

[TFT444]

Objective

Make the documented full local verification command produce the same formatting result on Windows and Ubuntu by enforcing repository line-ending policy.

Audit finding

GitHub CI passes ruff format --check . on Ubuntu, but this Windows checkout has core.autocrlf=true, no .gitattributes, and the same command reports 22 tracked Python files as requiring reformatting. Lint, strict mypy, 556 tests, and 100% coverage pass; the mismatch is line-ending normalization, not logic.

Scope

• Add minimal .gitattributes policy for text and binary assets.
• Normalize tracked text mechanically without semantic changes.
• Confirm Windows and Ubuntu use the same LF content.
• Document one-time renormalization for existing checkouts.
• Mark media and binary evidence as binary.

Acceptance criteria

• ruff format --check . passes on a fresh Windows checkout with core.autocrlf=true.
• Ubuntu CI remains green.
• Normalization has no semantic source changes.
• Lint, mypy, tests, and coverage remain unchanged.
• PNG, MP4, and other binaries are not rewritten.
• Contributor docs state supported line-ending behavior.
• A practical regression check prevents accidental CRLF reintroduction.

Non-goals

Broad restyling, changing Ruff rules, or changing runtime behavior.

Keywords

gitattributes line-endings windows ruff-format ci-parity