Record viewport associations for new dimensions

Removes PR3's `viewport_frame` seam in `viewport_ref.rs`; the frame is
PR1's camera-derived one everywhere.

The five dimension commands (DIMLINEAR / DIMALIGNED / DIMRADIUS /
DIMDIAMETER / DIMANGULAR) now record a real association when they
measure through a viewport. The commit path's one association gate
(`dimension_association_allowed`, added when PR2 was stacked) gains an
else-branch: where PR2 committed the dimension unassociated and PR1's
inference guard returned an empty source list, `Scene::attach_viewport_
dimension_association` now stores the whole chain — dimension ->
viewport -> block path -> entity -> feature — from the AcceptedSnaps PR1
captured, in definition-point slot order.

* `Scene::dimension_association_slot_points` names that order, including
  the radial dimensions `dimension_reference_points` does not cover.
* `OpenCADStudio::viewport_dimension_snaps` builds the slot array. A snap
  whose paper point is no longer the definition point it fills has its
  model point recomputed from that definition point through the frame:
  the object pick records one click for both extension origins, and a
  rotated DIMLINEAR projects its origins onto the measuring axis.
* Radial dimensions take their own path inside
  `attach_viewport_dimension_association`. Their single reference is an
  osnap type 10 carrying the radial marker (which circle / which polyline
  arc segment) and the angle around it; `source_reference` would hand
  back the generic curve-parameter marker -2, which
  `radial_source_for_marker` cannot find.

One measurement rule, documented in `viewport_ref::measurement_rule`:
`actual_measurement` is always the RAW measurement in the dimension's own
space (paper, for a viewport dimension), and the viewport compensation
lives only in the magnitude of the negative DIMLFAC override, applied
once by the formatter. PR2's persistence already followed it; PR3's
refresh did not — it substituted the model distance times
`model_factor()`, which made a refreshed dimension read `user_lfac` times
too much versus an identical freshly-created one. Refresh now writes the
paper measurement (a debug assert pins resolved paper points to the model
points through the frame), and `axis_distance` goes with it.

Block sub-entity snaps: verified that `block_cache` stamps the top-level
INSERT's handle onto every expanded and clipped sub-wire, so
`wire_source` can only ever report the INSERT — nested inserts included.
`OpenCADStudio::resolve_source_block_path` now descends from that INSERT
at accept time (using the object-pick path's existing
`resolve_measurable_entity`, so arbitrary depth, not just one level) and
fills `SnapSourceRef.block_path` with the real inner entity. Where the
descent cannot identify one — a non-planar-pickable type such as text,
hatch, spline or solid, or nesting past eight levels — the source stays
the INSERT with an empty path, which is coarser but never wrong. Both the
limitation and where it bites are documented on
`Scene::resolve_block_snap_source` and `SnapResult::source`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/app/dim_viewport.rs

@@ -183,6 +183,83 @@ impl OpenCADStudio {
         }
     }
 
+    /// The slot array [`Scene::attach_viewport_dimension_association`] wants,
+    /// built from the snaps PR1 recorded for the command that just committed
+    /// `dimension`.
+    ///
+    /// Slot `k` describes the feature at
+    /// `Scene::dimension_association_slot_points()[k]`, so the measuring snaps
+    /// are taken in collection order and truncated / padded to that length.
+    ///
+    /// A snap whose paper point is not (still) the definition point it would
+    /// fill has its `model_point` recomputed from that definition point
+    /// through the frame. Two cases need it:
+    ///
+    /// * the explicit object pick, which records one click twice — once per
+    ///   extension origin — so neither recorded point is the endpoint the
+    ///   command derived from the entity;
+    /// * a point the command moved after the snap (a rotated DIMLINEAR
+    ///   projects its origins onto the measuring axis).
+    ///
+    /// The source identity is kept in both cases: it is the entity that was
+    /// acquired, and the feature marker is re-derived from the corrected
+    /// point.
+    pub(crate) fn viewport_dimension_snaps(
+        &self,
+        i: usize,
+        dimension: Handle,
+    ) -> Vec<Option<AcceptedSnap>> {
+        let slots = self.tabs[i].scene.dimension_association_slot_points(dimension);
+        if slots.is_empty() {
+            return Vec::new();
+        }
+        let measuring = self.dimension_measuring_snaps(i);
+        slots
+            .iter()
+            .enumerate()
+            .map(|(index, slot)| {
+                let snap = measuring.get(index)?.clone();
+                let frame = snap.frame?;
+                let slot = DVec3::new(slot.x, slot.y, slot.z);
+                if snap.paper_point.truncate().distance_squared(slot.truncate()) <= 1e-12 {
+                    return Some(snap);
+                }
+                Some(AcceptedSnap {
+                    paper_point: slot,
+                    model_point: frame.paper_to_model(slot),
+                    ..snap
+                })
+            })
+            .collect()
+    }
+
+    /// Record the viewport association for a dimension that has just been
+    /// committed while measuring through a layout viewport.
+    ///
+    /// Announces the whole chain — the viewport, every INSERT on the block
+    /// path and the source entity — so the dependency index picks the new
+    /// association up immediately.
+    pub(crate) fn attach_viewport_dimension_association(&mut self, i: usize, dimension: Handle) {
+        let snaps = self.viewport_dimension_snaps(i, dimension);
+        if snaps.iter().flatten().all(|snap| snap.source.is_none()) {
+            return;
+        }
+        self.tabs[i]
+            .scene
+            .attach_viewport_dimension_association(dimension, &snaps);
+        let mut changes = vec![(dimension, crate::scene::ChangeKind::Modified)];
+        changes.extend(
+            self.tabs[i]
+                .scene
+                .dimension_association_sources(dimension)
+                .into_iter()
+                .map(|handle| (handle, crate::scene::ChangeKind::Modified)),
+        );
+        changes.sort_by_key(|(handle, _)| handle.value());
+        changes.dedup_by_key(|(handle, _)| handle.value());
+        self.tabs[i].scene.bump_entities(&changes);
+    }
+
     /// Apply viewport compensation to a dimension about to be committed.
     ///
     /// Whether the dimension may also take a paper-space association is a