🧰 Modernize project tooling, CI, and documentation

[frenck]

Proposed Changes

• Migrate project metadata from [tool.poetry] to PEP 621 [project] table with Poetry v2 (poetry-core>=2.0)
• Replace mypy with ty for type checking, pre-commit with prek, and add zizmor for GitHub Actions workflow auditing
• Migrate test mocking from aresponses to aioresponses
• Add Python 3.14 support to classifiers, CI test matrix, and DevContainer
• Pin all GitHub Actions with SHA digests, add persist-credentials: false and permissions to all workflows
• Add new workflows: dependency-review, OpenSSF Scorecard
• Add SBOM generation (CycloneDX) and Sigstore attestation to the release pipeline
• Add SECURITY.md, upgrade Code of Conduct to Contributor Covenant 3.0, convert issue templates to YAML forms
• Remove SonarCloud, stale bot, and CodeQL in favor of Scorecard; add OpenSSF Scorecard badge
• Raise coverage target to 95%, expand keywords for PyPI discoverability, bump copyright year to 2026
• Fix spelling and grammar across docstrings, README, and community files