Complete Dimension host model coverage for all nine subtypes

Adds a hand-written flat Dimension model to the adapter (manifest
manual_kinds hook) and a synthetic-property section to the host coverage
policy. The host derives actual_measurement and the base definition point on
scripted create/edit. staged_python_dimension_lifecycle_over_real_ipc passes
the full gate for every subtype including DWG and DXF reopen. Python ints are
now accepted for coordinates and angles.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugins/opencad-python/entity_manifest.json

@@ -23,8 +23,10 @@
     "AttributeEntity",
     "Hatch",
     "Leader",
-    "MLine"
+    "MLine",
+    "Dimension"
   ],
+  "manual_kinds": ["Dimension"],
   "base_fields": ["handle", "layer", "owner_handle"],
   "overrides": {
     "Point": {