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/README.md

@@ -94,7 +94,7 @@ The host-owned catalog classifies all 48 entity variants and tracks every
 traced field, including fields marked `unmapped`. Query it with
 `doc.coverage()` or `doc.coverage("Line")`; each row includes source field,
 type, access, and current validation status. Geometry edits remain limited to
-the 24 mapped kinds.
+the 25 mapped kinds.
 For any entity, `entity.snapshot` returns a detached dictionary of its raw
 CAD fields, including `snapshot["common"]` and kind-specific nested values.
 It can inspect an unmapped kind; editing the dictionary does