feat: DDEDIT command and double-click text editing

Add DDEDIT (ED alias) command that edits Text/MText/Attribute entities
in-place via the command line. Double-clicking a text entity in model space
now auto-launches DDEDIT for that entity. Supports Text, MText,
AttributeDefinition, and AttributeEntity types.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/annotate/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod aligned_dim;
 pub mod angular_dim;
+pub mod ddedit;
 pub mod diameter_dim;
 pub mod dim_baseline;
 pub mod dim_continue;