feat(styles): dimension, text and multileader styles on both engines; $DIMSTYLE/$TEXTSTYLE reach new entities headlessly

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

backends/base.py

@@ -33,6 +33,7 @@ from backends.contracts import (
     PremiumContract,
     SettingsContract,
     SolidContract,
+    StylesContract,
     SystemContract,
     TransactionContract,
     ViewContract,
@@ -184,6 +185,7 @@ class AutoCADBackend(
     PremiumContract,
     GdtContract,
     SettingsContract,
+    StylesContract,
 ):
     """All backends implement this interface.