feat(dyn): locked input fields constrain the preview and the click (#356)

A typed dynamic-input value (TAB-locked angle or distance) now shapes
the rubber-band: the cursor point is routed through dyn_resolve_point —
the same resolution Enter commits — in the mouse-move preview and the
click commit, so a locked 30° pins the line's direction while the free
field keeps tracking the cursor. The lock wins over osnap/ortho/polar.
TAB (and the comma advance) reshape the preview immediately instead of
waiting for the next mouse move.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/update/dynamic.rs

@@ -581,6 +581,15 @@ impl OpenCADStudio {
         if self.tabs[i].active_cmd.is_none() {
             return;
         }
+        // Re-resolve through the locked dyn fields first so a freshly typed
+        // value reshapes the preview immediately, without waiting for the
+        // next mouse move (#356). Idempotent for the polar/cartesian arms, so
+        // feeding the already-resolved cursor back in is stable.
+        if self.tabs[i].dyn_fields.iter().any(|f| f.buffer.is_some()) {
+            if let Some(r) = self.dyn_resolve_point() {
+                self.tabs[i].last_cursor_world = r;
+            }
+        }
         let cur = self.tabs[i].last_cursor_world;
         let previews = self.tabs[i]
             .active_cmd