Plan display file actions in app core

docs/modernization/build-inventory.md

@@ -430,6 +430,9 @@ Known local toolchain state:
   JSON for empty and non-empty file picker results; live image/file/save/
   directory picker branches consume the same contract before invoking retained
   platform callbacks or legacy picker bridges.
+- `pano_cli plan-display-file` exposes `pp_app_core` external file presentation
+  planning as JSON for empty and non-empty paths; the live display-file command
+  consumes the same contract before retained platform open-file bridges.
 - `pano_cli plan-cloud-upload` exposes `pp_app_core` cloud upload availability,
   new-document warning, publish prompt, and save-before-upload planning as JSON;
   the live cloud upload command consumes the same start contract before
@@ -461,7 +464,8 @@ Known local toolchain state:
 - `pp_app_core_document_sharing_tests` covers saved-path gating before platform
   share execution.
 - `pp_app_core_document_platform_io_tests` covers empty selected-path filtering
-  and non-empty picked-path callback planning before platform picker callbacks.
+  and non-empty picked-path callback planning, plus empty/non-empty display-file
+  planning before platform picker/display callbacks.
 - `pp_app_core_document_cloud_tests` covers cloud upload no-canvas,
   new-document warning, clean publish prompt, and dirty save-before-upload
   decisions, plus cloud browse no-canvas/show-browser and selected-download