docs: establish integrated project memory

.project-docs/05-agent-entry/integration-gate.md

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+# Integration Gate
+
+Use this gate to promote completed task facts into canonical project memory.
+
+## Requirements
+
+- Run in an exclusively owned integration worktree.
+- Hold the repository integration lock.
+- Verify the task commits being integrated are present.
+- Review source task records, task-prefixed supporting records, promotion candidates, and semantic conflicts in read-only mode.
+- Write integration notes only to the integration task's own task record or `{task_id}__<slug>.md` supporting records.
+- Ask before changing architecture direction, product behavior, or accepted decisions.
+- Record source task or merge commits under `Integrated Through` in `current-state.md`.
+
+Do not resolve meaningful document conflicts with `ours`, `theirs`, or union merge rules.