Backlog Update

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Read `PROJECT_BACKLOG.md`, `PROJECT_MAP.md`, and `ARCHITECTURE_SOURCE_OF_TRUTH.md` if present.
Check for duplicate backlog items before adding a new one.
Add or update a backlog item before implementation starts.
Use a stable ID and do not renumber existing items.
Set the correct kanban state, route, source, priority, owner, and architecture impact.
If architecture changes are required, update linked docs in the same task or create a follow-up backlog item.
If the task is deferred or rejected, archive it with reason instead of silently dropping it.
If validation or review evidence is missing, say so explicitly before marking `DONE`.