docs: add inspect.software health badge

[Nayjest]

This PR adds the inspect.software health badge to the README.

Why this PR?
Your project ranks in the upper rating bands of our open-source health index (which measures maintainability, responsiveness, and security). This badge makes that standing objectively visible to your users. Our index is a free public good, and scores cannot be bought.

Technical details:

• No tracking: Static SVG served via GitHub's CDN. No JavaScript, no third-party tracking.
• No maintenance: The badge updates automatically after every inspection.
• Transparent: Links directly to your full report, based on our open methodology.

If you prefer to keep your README minimal, feel free to close this PR without replying. Your report will remain publicly available and up-to-date either way.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.57%. Comparing base (efcba2e) to head (91faa84).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1201   +/-   ##
=======================================
  Coverage   82.57%   82.57%           
=======================================
  Files          83       83           
  Lines       26174    26174           
=======================================
  Hits        21613    21613           
  Misses       4561     4561           

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