Simplify mise min_version to hard-only

[iwamot]

Summary

• Revert `.mise.toml` `min_version` back to the simple string form (hard default).
• Remove the custom regex manager for `.mise.toml` from `renovate.json`.
• CI keeps following mise releases via `MISE_VERSION` in the workflow (already tracked by `customManagers:githubActionsVersions`), so no coverage is lost.

🤖 Generated with Claude Code

[github-actions]

Dependency Review

✅ No vulnerabilities found.

Snapshot Warnings

⚠️: No snapshots were found for the head SHA c9c210b.

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Scanned Files

None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.96%. Comparing base (900ecbd) to head (c9c210b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   50.96%   50.96%           
=======================================
  Files          26       26           
  Lines        1244     1244           
  Branches      178      178           
=======================================
  Hits          634      634           
  Misses        606      606           
  Partials        4        4           

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