Implement live_ui phase 18 focused example alignment

[pcharbon70]

Summary

• align live_ui examples one-for-one with the root widget-focused example inventory
• retire the package-local demo surface and retarget preview/inspect/export/validate to the aligned ids
• update docs, validation, traceability, and integration coverage for the new aligned example model

Section Commits

• 347ee1de Implement live_ui phase 18 section 18.1
• 709a568a Implement live_ui phase 18 section 18.2
• 13863af4 Implement live_ui phase 18 section 18.3
• 2fe601a6 Implement live_ui phase 18 section 18.4

Validation

• cd packages/live_ui && mix test
• cd packages/live_ui && mix live_ui.validate --strict
• mix spec.traceability.generate live_ui
• mix spec.diffcheck
• mix spec.verify --debug still reports the existing repo-wide spec baseline (57 errors, 264 warnings) unrelated to this branch