Add cross-phase acceptance integration coverage

[pcharbon70]

Summary

• add an end-to-end cross-phase integration suite covering acceptance scenarios X-1 through X-8
• validate schema-driven load/edit/save with concurrent clients and deterministic lock conflicts
• validate render degradation fallback behavior, undo/redo coherence, divergence conflict handling, and workspace-boundary audit emission
• validate crash/restart checkpoint recovery and reproducible release artifact generation from identical inputs
• mark cross-phase acceptance checklist items X-1..X-8 complete in planning index

Validation

• mix test test/jido/document/cross_phase_acceptance_integration_test.exs
• mix test
• mix quality