Add a Drafting page for the rotation angle and the polar increment

Two drafting preferences had no proper home. The Drafting Settings dialog
displays the drafting rotation and offers only a Reset button — there was no
way to type an angle short of `SETVAR SNAPANG`. The polar tracking increment
existed in exactly one place: a pop-up hanging off the status-bar pill.

The rotation is a text field over an edit buffer rather than the value
itself, so clearing it to retype does not snap the crosshair to zero on the
way through; the buffer is reseeded whenever the value is restored from
behind it. Angles render without a trailing `.0`, matching how the polar
pop-up has always shown them — same kind of number, same reader.

Snap modes, grid spacing and object snap stay in Drafting Settings, where
they belong; the page links to it.

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

src/app/update/file.rs

@@ -452,6 +452,9 @@ impl OpenCADStudio {
         } else {
             0.0
         };
+        // The Options field edits a buffer rather than the value, so it has to
+        // be reseeded whenever the value is restored from behind it.
+        self.snap_angle_input = crate::app::settings::format_snap_angle(self.snap_angle_deg);
         // Ortho + running OSNAP are per-drawing (adopted from the header on
         // open / tab switch), not app-global, so they are not applied here.
         self.snapper.otrack_enabled = s.otrack;

src/app/update/mod.rs

@@ -6266,6 +6266,27 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            // Typed into freely; only committed when it parses, so clearing
+            // the field to retype does not snap the crosshair back to zero.
+            Message::SnapAngleInputChanged(value) => {
+                self.snap_angle_input = value;
+                if let Ok(angle) = self.snap_angle_input.trim().parse::<f32>() {
+                    if angle.is_finite() {
+                        self.snap_angle_deg = angle.rem_euclid(360.0);
+                        self.persist_settings_if_changed();
+                    }
+                }
+                Task::none()
+            }
+
+            Message::PolarIncrementChanged(deg) => {
+                if deg.is_finite() && deg > 0.0 {
+                    self.polar_increment_deg = deg;
+                    self.persist_settings_if_changed();
+                }
+                Task::none()
+            }
+
             Message::PickDragRectToggled(rectangle) => {
                 self.pick_drag_rect = rectangle;
                 self.persist_settings_if_changed();