docs: refresh README

[roxblnfk]

Q	A
Bugfix?	❌
Breaks BC?	❌
New feature?	❌
Issues	—

• New header: centered RoadRunner logo, tagline, Documentation / Sponsor badges, then Psalm level / type coverage badges from Shepherd, and a short intro linking the Lock plugin docs.
• ## Get Started groups Requirements, Installation (with packagist badges), a minimal .rr.yaml and a first lock example; the existing method docs follow under ## Usage. The License section is removed.
• Dropped the Codecov badge (the last upload is from July 2024, the shared phpunit workflow gets no CODECOV_TOKEN), workflow status badges and the Discord badge.
• "Check lock" now matches the API: exists() returns bool and takes an optional lock id; the updateTTL() example says it sets the TTL (the plugin replaces it) instead of adding to it.

The Requirements list is untouched, so this merges cleanly with #10.

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