[Docs] Add software health index 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.

Summary

Adds one line to the README badge row. No code changes.

Test plan

README-only; no dependent tests. Rendering verified on the branch.

Benchmark / NCU (kernel changes only)

Neutral — no kernel changes.

Breaking changes

None.

Checklist

• I have read CONTRIBUTING.md and follow its conventions (code style, docstrings, commit prefixes).
• I have read AGENTS.md and, where my change matches its scope, the relevant skill under .agents/skills.
• This is not a minor/cosmetic-only PR (typo, formatting, style-only tweaks).
• Dependent tests pass locally or in CI; new behavior is covered by tests where applicable.
• Kernel changes include same-hardware before/after benchmark numbers (dense + varlen where applicable).

If you cannot tick the "not minor" box above

The "no busywork" rule is aimed at typos and style churn, and it's a good rule. This isn't that: it adds a link to an independent health report for this repository — public methodology, versioned, recomputed on every scan — so readers can check the project's standing rather than infer it. One line, trivially reversible.