feat: ATTEDIT — edit block attribute values interactively

- attedit.rs: AtteditCommand picks an INSERT entity then iterates through
  each attribute tag prompting for a new value (Enter keeps existing)
- attedit_pending_handle() / attedit_set_attrs() trait methods inject
  attribute data into the command after entity-pick (avoids document access
  in the command itself)
- cmd_result.rs: NeedPoint handler injects attr data; ReplaceEntity detects
  the __ATTEDIT__ sentinel and calls apply_attedit() on the document
- apply_attedit() encodes tag/value pairs as __ATTEDIT__tag\x01val\x02...
- ROADMAP.md: ATTEDIT marked ✅

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

ROADMAP.md

@@ -127,7 +127,7 @@ Underlay (PDF/DWF/DGN)
 | STRETCH (SS) | ✅ | — |
 | SPLINEDIT | ✅ CLOSE/OPEN/REVERSE + grip editing | — |
 | HATCHEDIT | ✅ | — |
-| ATTEDIT | ⬜ | Attribute değerlerini düzenleme |
+| ATTEDIT | ✅ Interactive tag-by-tag value editing | — |
 | DDEDIT (çift tık metin) | ✅ | — |
 | REFEDIT | ⬜ | Block in-place düzenleme |
 | DIVIDE (DIV) | ✅ | — |