feat: Dynamic Input overlay (DYNMODE / F12)

- overlay.rs: dynamic_input_overlay() canvas widget draws a semi-transparent
  coordinate tooltip near the cursor; shows X/Y in absolute mode or
  dist/angle relative to last_point when a command base point exists
- statusbar: DYN toggle pill with F12 tooltip (calls ToggleDynInput)
- app/mod.rs: dyn_input: bool field (default true), ToggleDynInput message
- view.rs: builds DYN label and pushes overlay into viewport_stack when
  dyn_input=true and a command is active
- document.rs: last_cursor_screen: iced::Point — updated on every ViewportMove
- ROADMAP.md: Dynamic Input overlay marked ✅

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

ROADMAP.md

@@ -197,7 +197,7 @@ Underlay (PDF/DWF/DGN)
 | Named UCS kaydetme | ⬜ |
 | VPORTS (viewport bölme) | ⬜ |
 | Nesne snap izleme (Object Snap Tracking) | ⬜ |
-| Dynamic Input overlay | ⬜ |
+| Dynamic Input overlay | ✅ F12 toggle, absolute XY + relative dist/angle |
 
 ---