feat(block-editor): wire Rotation, Alignment and Flip parameter placement

Enable the existing palette rows and BPARAMETER choices. Rotation accepts a
center, picked or numeric radius, and picked or numeric default angle.
Alignment places a tangent direction from its base point. Flip places a
reflection line and state label, with native grip and state expressions.

Extend shared graph append/capacity checks for Flip's additional state node
while preserving existing subgraphs. Keep Polar/Rotation angle labels unique
in either placement order. Add editor graphics, extents and definition
reframing through the existing overlay/history/save paths.

This milestone implements native parameter placement and persistence.
Rotate/Flip action association, reference alignment/grip editing, parameter
property editing and parameter sets remain separate work.

Validation covers command and palette placement, cancellation, local/parent
undo, save/discard, native DWG/DXF objects, existing graph preservation and
the 17 research fixtures. Broader block/dock regressions and editor renders
are also checked.

src/ui/overlay.rs

@@ -1019,6 +1019,7 @@ pub(crate) fn selection_overlay<'a>(
 
 pub(crate) struct AuthoringDimension {
     pub lines: Vec<[Point; 2]>,
+    pub round_grips: Vec<Point>,
     pub dimensions: Vec<[Point; 2]>,
     pub labels: Vec<(Point, String)>,
     pub grips: Vec<(Point, Option<Point>)>,
@@ -2410,6 +2411,9 @@ impl canvas::Program<Message> for SelectionCanvas {
                         ..Default::default()
                     });
                 }
+                for point in &dimension.round_grips {
+                    frame.fill(&canvas::Path::circle(*point, 3.5), color);
+                }
                 for (point, base) in &dimension.grips {
                     let marker = if let Some(base) = base {
                         let dx = point.x - base.x;