Export venues as editor-authorable .tres resources

- tools/export_venues.gd (SceneTree script) saves the three factory scenarios to
  content/venues/<id>.tres via ResourceSaver. The factory stays the source of truth;
  the exported files are what an editor workflow would edit and ship.
- New tests load the files back and check that id, name, event pool, profiles,
  policy (ID/wand), equipment, door-staff lines, shift phases, and locations all
  survive. They also fail when the exported files are missing or stale, so the
  export is re-run after content changes.
- GUT is consciously not adopted: the custom headless runner already covers 157
  assertions without an editor plugin and keeps CI dependency-free. Recorded in
  DONE.md.
- TODO: the planned backlog is complete; only optional future ideas remain.
- README/MEMORY updated. Version 0.2.16.

project.godot

@@ -8,7 +8,7 @@ config_version=5
 
 config/name="Step Line"
 config/description="Workplace security simulation about observation, access verification, and proportionate escalation."
-config/version="0.2.15"
+config/version="0.2.16"
 run/main_scene="res://scenes/main.tscn"
 config/features=PackedStringArray("4.3", "GL Compatibility")