chore(deps-dev): Update ruff requirement from >=0.12.0 to >=0.15.21 (#131)

Updates the requirements on [ruff](https://github.com/astral-sh/ruff) to permit the latest version.
- [Release notes](https://github.com/astral-sh/ruff/releases)
- [Changelog](https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md)
- [Commits](astral-sh/ruff@0.12.0...0.15.21)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.21
  dependency-type: direct:development
...

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Author: dependabot[bot]

pyproject.toml

@@ -15,7 +15,7 @@ python-preference = "managed"
 # Dev tools are added in Epic 2; groups reserved so root tasks stay stable.
 [dependency-groups]
 dev = [
-    "ruff>=0.12.0",
+    "ruff>=0.15.21",
     "pyright>=1.1.400",
     "pre-commit>=4.0.0",
     "pytest-cov>=6.0.0",