Reconcile issue #35 self-update feature

[dapi]

Summary

• confirm the existing Go self-update implementation satisfies issue Add self-update command for installed CLI #35: both entry points, release lookup, no-downgrade behavior, verified replacement, and outside-git operation
• reconcile issue Add self-update command for installed CLI #35 with the existing FT-013 delivery slice and migrate it to current feature-flow owners
• replace stale Bash-era references with current Go runtime grounding and close the feature lifecycle with concrete evidence

Validation

• make test
  • go vet ./...
  • go test ./...
  • python3 scripts/check_memory_bank_index.py --max-depth 4
  • git diff --check
• thread-aware PR review scan: no comments or unresolved review threads

Closes #35