ci: update setup actions to v7

[TIMtechnology]

Summary

• update actions/setup-node to v7.0.0 at its verified full commit SHA
• update actions/setup-python to v7.0.0 at its verified full commit SHA
• keep the runtime matrix unchanged: Node.js 20.19 and Python 3.12
• supersede Dependabot PRs build(deps): bump actions/setup-node from 5.0.0 to 7.0.0 #9 and build(deps): bump actions/setup-python from 6.3.0 to 7.0.0 #10, whose branches no longer merge cleanly with current main

Risk boundary

This changes GitHub Actions runtime dependencies only. It does not modify application dependencies, production code, weather data, model artifacts, deployment workflows, or production services.

Verification

• bash scripts/validate-release.sh
• backend: 39 tests passed
• dependency audits: no known Python vulnerabilities; npm audit reports 0 vulnerabilities
• frontend type check and production build passed
• ML reviewed-artifact validation passed