Add document export file automation

docs/modernization/roadmap.md

@@ -355,6 +355,8 @@ bytes using that writer, including PNG-encoded layer/frame face payloads.
 `pano_cli simulate-document-export` exercises that pure document export path,
 decodes the generated PPI bytes, reimports them, and emits JSON round-trip
 metadata.
+`pano_cli save-document-project` writes the same pure document export to a PPI
+file for inspect/load round-trip automation.
 `pano_cli create-document` can create simple animation documents with explicit
 frame count/duration. `pano_cli simulate-document-edits` exercises pure
 layer metadata, frame reordering, active-index preservation, tiny face-payload
@@ -364,6 +366,8 @@ summaries. `pano_cli simulate-image-import` decodes an embedded tiny PNG
 through `pp_assets` and attaches the resulting RGBA8 payload to `pp_document`.
 `pano_cli simulate-document-export` exercises pure document-to-PPI export,
 asset-level PPI image decode, and document reimport in one automation command.
+`pano_cli save-document-project` writes a deterministic pure document export
+PPI and verifies it through inspect/load smoke coverage.
 `pano_cli simulate-stroke` exercises the pure stroke sampler for
 scripted-stroke automation. `pano_cli simulate-stroke-script`
 loads stroke script fixtures, parses them through `pp_paint`, and samples every
@@ -746,6 +750,9 @@ Results:
   `pp_assets` PPI writer can save a compressed RGBA PNG dirty-face payload to
   an explicit layer/frame slot, inspect the serialized descriptor, and reload
   it as decoded `pp_document` face-pixel data.
+- `pano_cli_save_document_project_roundtrip_smoke` passed and proves a pure
+  `pp_document` export can be written to a PPI file, inspected for layer/frame
+  dirty-face descriptors, and loaded back through the PPI import path.
 - `pano_cli_parse_layout_smoke` passed.
 - `pano_cli_simulate_stroke_smoke` passed and reports deterministic stroke
   sample counts/distances.
@@ -824,6 +831,8 @@ Results:
   by DEBT-0010/DEBT-0013.
 - `pano_cli simulate-document-export` exposes the same export path through JSON
   automation for agents.
+- `pano_cli save-document-project` exposes file-writing document export
+  automation for inspect/load round trips.
 - Snapshot creation now rejects invalid embedded RGBA8 face payloads before
   document export or history can persist malformed state.
 - PowerShell package-smoke wrapper validates the Windows CMake app executable