Load PPI metadata into documents

docs/modernization/build-inventory.md

@@ -91,7 +91,7 @@ Known local toolchain state:
   `pp_paint`, `pp_document`, `pp_renderer_api`, `pp_paint_renderer`,
   `pp_ui_core`, `pano_cli`, and their current headless test binaries,
   including foundation event/logging/task queue coverage, PNG metadata, PPI
-  header/layout, settings document, document frame move/duration coverage,
+  header/layout, settings document, document snapshot/frame move/duration coverage,
   paint brush/stroke/stroke-script coverage, renderer shader descriptor
   coverage, UI color parsing, and layout XML parse coverage.
 - `pano_cli inspect-image` reports PNG IHDR metadata as JSON and is covered by
@@ -100,6 +100,9 @@ Known local toolchain state:
   body summary fields, layer/frame descriptors, and dirty-face PNG payload
   metadata, and is covered by `pano_cli_inspect_project_layout_smoke` with a
   minimal PPI fixture.
+- `pano_cli load-project` creates a metadata-only `pp_document` projection for
+  representable PPI timelines and is covered by
+  `pano_cli_load_project_metadata_smoke`.
 - `pano_cli create-document` supports `--frames` and `--frame-duration-ms` and
   is covered by `pano_cli_create_animation_document_smoke`.
 - `pano_cli simulate-stroke` exposes the pure stroke sampler for scripted