Improve admin UX workflows

[AJFrio]

Summary

• improve admin navigation responsiveness and normalize fulfillment URLs
• add product deep links, dirty-state handling, unsaved-change prompts, and themed delete dialogs
• make collections, media, fulfillment, and store settings controls more explicit and consistent

Validation

• npm run harness:validate
• npm test -- --run
• npm run build
• npx eslint changed admin/backend files (0 errors, existing hook warnings only)

Notes

• Full npm run lint still fails on pre-existing unrelated unused-variable errors across scripts, tests, and components outside this change.