WCN-2441: Run CI against Node Current, Active LTS, and Maintenance LTS

[gokulhost]

Summary

• Adds Node's Current release line (26.x) to the unit-test CI matrix alongside the required Active LTS (24.x) and Maintenance LTS (22.x) versions.
• The 26.x leg runs with continue-on-error so failures don't block merge — it's not an LTS version yet.
• A failure on the Current leg posts (or updates) a PR comment so it isn't silently missed; the comment is cleared once it passes again.
• Documents the bump process in README.md: when a Node major is promoted to Active LTS, move it into the required matrix set, add the new Current release, and bump engines.node across modules.

Stacked on #9614 (WCN-2442, drops EOL Node 20) — this PR only adds the Current leg + comment automation on top.

Follow-up ticket for automating the Current/Active/Maintenance detection itself (rather than hardcoding version numbers): WAL-2001 (good-for-intern).

Test plan

• Validated ci.yml YAML syntax
• CI passes: 22.x/24.x required, 26.x non-blocking
• Manually verify PR comment posts on a forced 26.x failure, then clears on a following green run

Ticket: WCN-2441

[linear-code]

WCN-2441