Phase 3: mixed-source combined Analyze

[Paul Lizer (paullizer)]

Summary\n\n- Add default-off �nable_mixed_source_analyze orchestration for explicit combined Analyze selections.\n- Reuse the Phase 1 authorized source manifest, capability partitions, bounded evidence envelopes, existing document-window analysis, and tabular document-action runner.\n- Run narrative and tabular cohorts through native engines, preserve tabular artifacts/citations, then perform one bounded coverage-aware collective reduction.\n- Keep per-document Analyze separate; flag-off mixed selections now fail with a clear temporary limitation rather than silently falling back to table-as-text behavior.\n- Add Phase 3 feature documentation, release note, regression coverage, and bump the application version to