docs: publish portable plan naming convention

[achangkuon]

Summary

• publishes a versioned, portable Plan → Session → Module → Task convention
• defines the overflow rule for chained PRs by Module under one Session
• distinguishes planning vocabulary from Control Tower domain and commit-grouping exceptions
• removes machine-specific paths as a required source of truth

Verification

• git diff --check
• documentation-only change

This PR must not be merged without Emilio’s authorization.