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).

Tools/tests/test_ue_common.py

@@ -0,0 +1,70 @@
+"""Tests for Tools/ue_common.py — the shared Unreal commandlet helpers.
+
+Pure stdlib: these helpers exist to turn two silent failures into loud ones, so
+they are tested without starting Unreal.
+"""
+
+import os
+import stat
+import sys
+import tempfile
+import unittest
+
+ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", ".."))
+sys.path.insert(0, os.path.join(ROOT, "Tools"))
+
+import ue_common  # noqa: E402
+
+
+class MakeWritableTest(unittest.TestCase):
+    def test_read_only_file_is_made_writable(self):
+        # Exactly how an LFS-tracked .umap checks out: 0o444.
+        with tempfile.NamedTemporaryFile(delete=False) as handle:
+            path = handle.name
+        try:
+            os.chmod(path, 0o444)
+            self.assertFalse(os.access(path, os.W_OK))
+            note = ue_common.make_writable(path)
+            self.assertIsNotNone(note)
+            self.assertIn("chmod u+w", note)
+            self.assertTrue(os.access(path, os.W_OK))
+        finally:
+            os.chmod(path, 0o644)
+            os.unlink(path)
+
+    def test_writable_file_reports_nothing(self):
+        with tempfile.NamedTemporaryFile(delete=False) as handle:
+            path = handle.name
+        try:
+            os.chmod(path, 0o644)
+            self.assertIsNone(ue_common.make_writable(path))
+        finally:
+            os.unlink(path)
+
+    def test_missing_file_raises(self):
+        # A typo must not look like a permissions problem.
+        with tempfile.TemporaryDirectory() as tmp:
+            with self.assertRaises(FileNotFoundError):
+                ue_common.make_writable(os.path.join(tmp, "absent.umap"))
+
+    def test_read_bits_are_preserved(self):
+        with tempfile.NamedTemporaryFile(delete=False) as handle:
+            path = handle.name
+        try:
+            os.chmod(path, 0o400)
+            ue_common.make_writable(path)
+            mode = os.stat(path).st_mode
+            self.assertTrue(mode & stat.S_IRUSR)
+        finally:
+            os.chmod(path, 0o644)
+            os.unlink(path)
+
+
+class RequireSavedTest(unittest.TestCase):
+    def test_passes_the_save_result_through(self):
+        self.assertTrue(ue_common.require_saved(True, "/Game/X"))
+        self.assertFalse(ue_common.require_saved(False, "/Game/X"))
+
+
+if __name__ == "__main__":
+    unittest.main()