chore: define uv version once in pre-commit config

[adamtheturtle]

Matches the pattern from literalizer: a YAML anchor .uv_version so the uv pin is declared once and referenced as *uv_version in each hook's additional_dependencies.

pre-commit validate-config may warn about an unexpected root key .uv_version; that is expected and matches literalizer.

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Note

Low Risk
Low risk config-only refactor that should not change behavior, but YAML anchors/extra root key may affect strict config validators.

Overview
Introduces a single .uv_version YAML anchor in .pre-commit-config.yaml and replaces repeated additional_dependencies: [uv==0.9.5] entries with references to [*uv_version] across all local hooks.

This centralizes the uv pin to reduce duplication and make future version bumps a one-line change.

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