Sync Phase 48 queue truth

[YSCJRH]

Summary

• sync tracked repo status docs so Phase 47 is closed and Phase 48 is the active approved successor queue
• add the Phase 48 successor-gate baseline and keep untracked planning files classified as candidate inputs only
• preserve public demo, private-beta, and Mirror Codex plugin boundaries without changing code or contracts

Validation

• python scripts/check_no_secrets.py
• python -m backend.app.cli audit-github-queue --repo YSCJRH/mirror-sim
• python -m backend.app.cli classify-lane --files README.md docs/plans/automation-roadmap.md docs/plans/current-state-baseline.md docs/plans/phase-47-successor-gate-2026-05-16.md docs/plans/phase-48-successor-gate-2026-05-17.md docs/plans/phase-execution-queue.md
• git diff --check
• git diff --cached --check

Fixes #376