fix(tools): importers clear the read-only LFS bit before saving; docs refresh

0.1.3 packaging and setup fixes from what 0.1.x actually exposed.

- New Tools/ue_common.py: make_writable() clears the read-only bit an LFS .umap
  checks out with (save_map() otherwise returns False silently and the staged actor
  is lost) and require_saved() makes that failure visible. ue_hero_facade_import and
  ue_import_north_buildings now call it; the map builders already did. Verified from
  a forced 0o444 map: chmod logged, save_map True, exit 0.
- Docs/build.md: pipeline table now lists the seven site FBXs plus frontage, north,
  hero and map steps and the shared FBX preset; packaging archive corrected to
  Builds/GigLineQA; packaged-log location and -qaselftest usage documented; new
  'Traps that cost real time in 0.1.x' table (read-only save, hero --out is the FBX,
  MPFB add-on path, shot actor quitting under QA, null-RHI trace trap).
- Docs/setup.md: fresh-checkout build marked verified 2026-11-08 and the blocker
  closed; new optional-keys section for OPENROUTER_API_KEY and MAPBOX_ACCESS_TOKEN
  (gitignored .env, not needed by build/tests/release).
- Docs/Architecture 07 + architecture.md: build-output path corrected, marked
  outside the repository.
- 5 new tests for ue_common (54 total).

MEMORY.md

@@ -507,3 +507,21 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
   scan: banners, windows and the parapet produce different edge sets at different
   heights and the pairwise match is meaningless (it reported a 418 px "drift").
   Verify it geometrically in the camera list instead.
+
+## 2026-11-09 — 0.1.3 packaging/setup fixes
+
+- **`Tools/ue_common.py`**: `make_writable()` clears the read-only bit an LFS
+  `.umap` checks out with (otherwise `save_map()` returns False with no error and
+  the staged actors vanish), and `require_saved()` makes that failure visible.
+  `ue_hero_facade_import.py` and `ue_import_north_buildings.py` never did this —
+  which is why importing the hero appeared to succeed while saving nothing.
+  Verified by forcing `chmod u-w` on DemoMap first: the run logged
+  `map writable: chmod u+w … (was 0o444)`, then `save_map: True`, exit 0.
+- Gotcha while adding it: `ue_hero_facade_import.py` had **no** `import os`/`sys`
+  (only `unreal`), so the sys.path line raised `NameError: name 'sys' is not
+  defined` inside the commandlet — an exit code of 255 with no obvious cause.
+- Docs: `build.md` gained the current pipeline table (7 site FBXs, frontage, north,
+  hero, map), the `Builds/GigLineQA` archive, the packaged-log path, `-qaselftest`
+  usage and a **traps** table; `setup.md` marks the fresh-checkout build verified and
+  documents the two optional API keys; architecture 07 + combined doc corrected the
+  build-output path.