Fix settings bridge reinitialization and about:blank handling

[YUMA-NAGAO]

Summary

• keep the isolated-world settings bridge available across disable/re-enable cycles
• answer every settings handshake with the current sanitized settings snapshot
• evaluate disabled-site rules and per-site speed against the creator URL for inherited about: frames
• use that inherited context for domain CSS and site-handler selection as well
• avoid early-handshake and re-enable races, and block runtime relays/storage writes while inactive

Testing

• npm ci
• npm run lint
• npm run build:release
• npm test (31 files, 396 tests)
• independent diff review and Codex second-opinion review

Notes

• No manifest permissions changed.
• npm audit --audit-level=high reports the same existing 9 advisories (4 high) on upstream/master and this branch; dependency updates are intentionally out of scope.