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/view/modal.rs

@@ -204,7 +204,9 @@ impl OpenCADStudio {
                             dimension_continue_mode: self.dimension_continue_mode,
                             qdim_snap_priority: self.quick_dimension_snap_priority,
                             annotation_auto_scale: self.annotation_auto_scale,
+                            polar_increment_deg: self.polar_increment_deg,
                         },
+                        &self.snap_angle_input,
                         self.double_click_block_refedit,
                         self.double_click_block_attedit,
                         self.cursor_type,