Bounded Residency: docs and release evidence

[flyingrobots]

Parent Goalpost

• v6.1.0: Bounded Residency #38

Work

Update design witness, STATUS.md, CHANGELOG.md, and issue closeout notes after the runtime slices land.

Expected Proof

• Witness file under docs/design/0045-v6-1-bounded-residency/witness/.
• Focused and full validation commands recorded.
• GitHub issue closeout links to PR evidence.

[flyingrobots]

Release-train update: this docs-and-evidence closeout moves from v6.3.1 to v6.4.1 because v6.4.0 is now the next published minor. No runtime scope or priority changed.