Add technical edit stage to Lanes 2 and 3

[AdamGohs]

Summary

• Update stage-progression workflow to route major revisions (Lane 2) through technical edit after Lead Civil review, and minor revisions (Lane 3) through technical edit after peer review
• Extend the PR description checkbox handler and admin override label to work for all three lanes with technical edit (Lane 1 advances to Director; Lanes 2 & 3 advance to ready-to-merge)
• Update PR template and implementation doc to reflect the new review stages

[github-actions]

✅ CI build passed for commit 3cc2b3e

This PR does not touch documentation content under docs/, so no multi-stage review is required.

@usace-rmc/docs-admin may merge.