docs: update Discord invite links to current working link

[devin-ai-integration]

docs: fix Discord invite link and migrate to genlayerlabs organization

Summary

This PR fixes a broken Discord invite link and migrates all GitHub organization references from yeagerai to genlayerlabs:

Discord Link Fix:

• README.md badge link: discord.gg/VpfmXEMN66 → discord.gg/qjCU4AWnKE (old link was expired/invalid)

GitHub Organization Migration:

• README.md: Updated Twitter badge URL and CONTRIBUTING link
• CONTRIBUTING.md: Updated 4 references (issue links, git clone command, docs repository link)
• LICENSE: Updated copyright from "YeagerAI LLC" to "GenLayer Labs"

Note: CONTRIBUTING.md uses a different Discord invite link (discord.gg/8Jm4v89VAu) which is still valid and was intentionally NOT changed per user request.

Review & Testing Checklist for Human

• Click the Discord badge link in README.md to verify it successfully opens the GenLayer Discord server (most critical - this was the broken link)
• Test GitHub organization links by clicking the CONTRIBUTING link in README.md and verifying it goes to github.com/genlayerlabs/genlayer-py
• Verify copyright change is authorized - confirm "GenLayer Labs" is the correct legal entity for the copyright

Notes

• The CONTRIBUTING.md files use discord.gg/8Jm4v89VAu instead of the new README link - this is intentional per user feedback, as that invite link is still valid
• This is a documentation-only change with no functional code impact
• CI passing confirms no syntax issues in markdown files

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Link to Devin run: https://app.devin.ai/sessions/96c0b3235fb2487e9df975192f257d56
Requested by: daniel@genlayerlabs.com (@danielrc888)

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