Add optimizer skill updates

[nodatall]

Summary

• add the no-flag page-speed optimizer skill with journey inventory, goal state, ledger, and stop conditions
• simplify backend optimizer invocation to one no-flag workflow
• add backend optimizer goal-state and shared ledger requirements

Validation

• quick_validate.py skills/page-speed-optimizer
• quick_validate.py skills/backend-optimizer
• python3 scripts/validate-skill-contracts.py
• git diff --check origin/main...HEAD
• ./scripts/install-codex-plugin.sh