feat(points): point style commands + DDPTYPE dialog, viewport-aware size

Points could only render as a 1px dot — no way to change PDMODE/PDSIZE.

- PDMODE / PDSIZE commands set the header value and rebuild the glyphs.
- DDPTYPE opens a Point Style dialog: a 5x4 grid of rendered glyphs
  (shape x enclosure), a size field, and relative/absolute radios.
- Relative (<=0) PDSIZE now sizes from the current world-per-pixel so the
  marker stays a roughly constant on-screen size across zoom, rebuilding
  on zoom via the existing camera-generation cache key. Absolute (>0)
  scales with the world as before. Switching to absolute with a zero size
  seeds a positive value from the on-screen size so it stays representable.

Part of the #100 extensibility epic (point style surfaced in #106).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/cache/block_cache.rs

@@ -450,7 +450,7 @@ fn tessellate_sub_local(
     // top-level MTEXT outside blocks the colour split is preserved via the
     // hot path in `tessellate_entity`.
     let mut wires_out = tessellate::tessellate(
-        doc, h, sub, false, sub_color, pat_len, pat, lw_px, local_offset, anno_scale,
+        doc, h, sub, false, sub_color, pat_len, pat, lw_px, local_offset, anno_scale, None,
     );
     if wires_out.is_empty() {
         return None;

src/scene/convert/tessellate.rs

@@ -42,6 +42,7 @@ pub fn tessellate(
     line_weight_px: f32,
     world_offset: [f64; 3],
     anno_scale: f32,
+    world_per_pixel: Option<f32>,
 ) -> Vec<WireModel> {
     let color = if selected {
         WireModel::SELECTED
@@ -87,7 +88,11 @@ pub fn tessellate(
     }
 
     // ── Try the truck path first ───────────────────────────────────────────
-    if let Some(te) = convert(entity, document) {
+    // Relative-PDSIZE points size their glyph from the current zoom so they
+    // stay a roughly constant on-screen size; otherwise the header-driven path.
+    let te = crate::entities::point::relative_truck(entity, document, world_per_pixel)
+        .or_else(|| convert(entity, document));
+    if let Some(te) = te {
         match te.object {
             // ── Text / MText: pre-tessellated glyph strokes ───────────────
             //

src/scene/mod.rs

@@ -7109,6 +7109,7 @@ fn tessellate_entity(
             1.5,
             world_offset,
             1.0,
+            world_per_pixel,
         );
         let ab = entity_aabb(e, world_offset);
         for w in &mut wires {
@@ -7423,6 +7424,7 @@ fn tessellate_entity(
                     sub_line_weight_px,
                     world_offset,
                     anno_scale,
+                    world_per_pixel,
                 );
                 for w in &mut wires {
                     w.name = h.value().to_string();
@@ -7584,6 +7586,7 @@ fn tessellate_entity(
         line_weight_px,
         world_offset,
         anno_scale,
+        world_per_pixel,
     );
     for b in &mut bases {
         b.aci = aci;