chore: bump Node.js minimum to v22

[rolginroman]

Summary

• Bump engines.node from >=18 to >=22 across root + all 7 packages (common, distributor, eslint-config, launchpad, staking, stream)
• CI test matrix [18, 20, 22, 24] → [22, 24] in version-tests.yml
• docs.yml Node 20 → Node 22
• setup-node composite already defaults to 22.14.0 (no change)

Why

• Node 18 reached end-of-life 2026-04-30
• Node 20 entered maintenance-only 2026-04, EOL April 2027
• Node 22 is current active LTS (Jod), maintenance through 2027-04, EOL 2027-04 → safe baseline through 2027
• Drops support surface, unlocks newer JS features

Test plan

• PR Checks workflow passes against Node 22 + 24 matrix
• Publish workflow alpha trigger succeeds
• No consumer breakage (semver-major engine bump — flagged in commit message)

Notes

• This is a breaking change for consumers running Node 18/20. Plan version bump to 13.0.0 on next stable release.