Enable the complete Pyflakes Ruff rule family

[Infiland]

Child scope of #795.

Problem

Ruff currently selects only E9, F63, F7, and F82, so most Pyflakes diagnostics are not enforced. Enabling the complete F family on current main reports exactly 10 findings across four files:

• one duplicate, identical "Data Structures Sequential" dictionary key (F601);
• nine constant f-strings with no placeholders (F541).

This is a small, reviewable first slice of the broader #795 maintainability baseline.

Scope

• Enable the complete Ruff F rule family while retaining the current correctness rules.
• Remove the duplicate identical manifest key.
• Remove only the redundant f prefixes from constant strings.
• Update workflow/configuration policy coverage and contributor guidance so full Pyflakes cannot regress silently.
• Do not enable import sorting, bugbear, McCabe, formatting, or unrelated style families in this child issue.
• Do not close Expand Ruff CI to enforce a maintainability baseline #795; its remaining rule families stay tracked there.

Acceptance criteria

• python -m ruff check --select F . and the repository's normal Ruff command both pass without blanket noqa suppressions.
• Generated sprite scenes, project settings, manifest output, and GUI presentation remain byte-for-byte or behaviorally unchanged as applicable.
• Focused workflow/documentation, manifest/architecture, project-settings, sprite/golden/Godot-validation, and GUI tests pass.
• ./venv/bin/pyright --warnings reports no errors or warnings.
• The full unit suite passes.
• Exact-head GameMaker LTS 2026 conversion and Godot 4.7.1.stable.official.a13da4feb gates remain green.