docs: correct static rule count in README to 34 of 42

[MaximeGaudin]

Summary

• The README claimed "twenty-nine of thirty-seven rules never touch a model"; the catalogue has since grown. Built the CLI and ran slint rules --json: 42 rules total, 8 need a model, 34 are static, 4 carry a fix. So the static/total ratio is 34 of 42, not 29 of 37. (The "eight rules" model count and the fixable count were already correct and are untouched.)
• Corrected README.md to "thirty-four of forty-two", keeping the file's word-form style.

Note: the docs-site landing copy (apps/docs/src/components/HomePillars.astro) already computes its counts dynamically from rules.json, so it was never stale — only the hardcoded README line needed fixing. The related rules-sync CI work (#186) keeps rules.json in lockstep with slint rules --json.

Fixes #106

Test plan

• Built slint-cli and ran slint rules --json; confirmed total=42, model=8, static=34, fixable=4.
• Grep confirms the stale "twenty-nine of thirty-seven" was the only hardcoded occurrence in source (the apps/docs/dist/index.html hit in the issue is a build artifact, regenerated from the dynamic component).
• README-only change.
• CI green on the PR