Dedupe Codex++ settings sidebar groups

[wananing]

Summary

• dedupe repeated Codex++ injected settings sidebar groups per sidebar slot
• adopt an existing Tweaks pages group before rebuilding it so state resets do not append another group
• add unit coverage for duplicate injected group selection

Closes #507

Validation

• node --import tsx --test packages/runtime/test/settings-sidebar-dedupe.test.ts
• npm test
• npm run build
• npm run audit (reports existing esbuild low and tar moderate advisories)