Add metadata-only PPI save automation

docs/modernization/build-inventory.md

@@ -115,6 +115,9 @@ Known local toolchain state:
   frame counts, durations, and decoded face-pixel payloads when present; the
   metadata-only minimal fixture remains covered by
   `pano_cli_load_project_metadata_smoke`.
+- `pano_cli save-project` writes metadata-only one-layer/one-frame PPI files
+  through `pp_assets` and is covered by `pano_cli_save_project_roundtrip_smoke`,
+  which reloads the generated project through `pano_cli load-project`.
 - `pano_cli create-document` supports `--frames` and `--frame-duration-ms` and
   is covered by `pano_cli_create_animation_document_smoke`.
 - `pano_cli simulate-document-edits` exercises pure document layer/frame edit
@@ -271,6 +274,9 @@ Known local toolchain state:
   face-payload attachment through JSON automation and is covered by
   `pano_cli_import_image_rejects_truncated_png`; a checked-in decodable image
   fixture and export/round-trip automation remain future CLI tasks.
+- `pano_cli save-project` exposes metadata-only PPI writing through JSON
+  automation and is covered by `pano_cli_save_project_roundtrip_smoke`; full
+  dirty-face payload save parity remains tracked by DEBT-0013.
 - `pp_ui_core` consumes vcpkg tinyxml2 only when `PP_USE_VCPKG_TINYXML2=ON`
   through the vcpkg preset; default and Android validation still use the
   retained vendored fallback tracked by DEBT-0012.