feat: Documentation Sync release step + portable project-week formula

[dbaratech]

Motivation

TRIP keeps its own docs (ARCHI.md, changelogs, CRs) in sync at release time, but the project's pre-existing documentation (README, contributor guides, ops manuals, reference specs) drifts silently: nothing in the flow ever asks "which docs does this feature leave stale?". After a few releases the README's command table or structure tree no longer matches the code.

This PR closes that gap with a plan-declared, release-enforced sync — plus a small portability fix for the project-week formula.

Changes

TRIP-1-plan — new mandatory Documentation Impact section in the plan template: the plan must list every non-TRIP document the feature will leave outdated (or state "None"). During Init the candidate list is adapted to the project's actual living docs. Also adds an optional Init-resolved prerequisites line for projects whose plans must respect additional living docs (e.g. an operations manual) with the condition under which each must be read.

TRIP-3-release — new Documentation Sync step (before the commit gate): read the plan's Documentation Impact, contrast it with the actual diff of the release (the plan may have fallen short), and update every affected doc. Guardrails: factual corrections only (commands, paths, tables, env vars, structure trees) — touching the voice, tone, or editorial content of those docs is forbidden. Synced files ride in the release commit, never a separate one. Subsequent steps renumbered.

Project-week formula — replaced date -d '[WEEK_ANCHOR_DATE]' with a python3 -c one-liner using date.fromisoformat: macOS BSD date doesn't support -d, so the previous formula only worked on GNU/Linux. The Init anchor-date command gets the same treatment, so both run identically on macOS and Linux.

TRIP-init — Phase 6 instructions and the post-init checklist updated to cover the two new adaptation points (Documentation Impact candidates, prerequisites line) and the renumbering when tutorials are enabled.

Notes

• No breaking changes for existing installs: projects that re-run Init (or apply TRIP-upgrade) pick the new sections up; the vanilla flow is otherwise unchanged.
• Tested by initializing TRIP on a real Next.js project (macOS): placeholders resolve cleanly and the week formula returns the correct week on BSD date systems.