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>

ROADMAP.md

@@ -128,7 +128,7 @@ Underlay (PDF/DWF/DGN)
 | SPLINEDIT | ⬜ | — |
 | HATCHEDIT | ⬜ | Var olan hatch'i düzenleme |
 | ATTEDIT | ⬜ | Attribute değerlerini düzenleme |
-| DDEDIT (çift tık metin) | ⬜ | In-place metin düzenleme |
+| DDEDIT (çift tık metin) | ✅ | — |
 | REFEDIT | ⬜ | Block in-place düzenleme |
 | DIVIDE (DIV) | ✅ | — |
 | MEASURE (ME) | ✅ | — |