[YanickSchraner]

Moves CI off python-backend-ci.yml, which ci-workflows v10.0.0 removed, to the shared mise-based ci.yml (pinned a7a5611 # v10.0.0).

• New mise.toml: uv 0.11.31 plus install, check, ci-check, test:unit and ci tasks. They call the same commands as before (the Makefile stays).
• The quality job is now ci.yml, which runs mise run ci-check. Python comes from .python-version via uv.
• Workflows get explicit token permissions (contents: read; the ci.yml and /documentation callers get what those reusable workflows need), which closes the CodeQL "Workflow does not contain permissions" alerts.

Verified locally: mise run ci-check and mise run test:unit pass.

Required check names change. The old <job> / Quality Checks and <job> / Tests & Type Checks checks no longer exist; the quality check is now <job> / CI (install & test). If the branch ruleset requires the old names, it must be updated before this PR can merge.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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  Coverage   96.71%   96.71%           
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  Files           7        7           
  Lines         457      457           
  Branches       62       62           
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  Hits          442      442           
  Misses         12       12           
  Partials        3        3