feat(app): record accepted snaps per point step and guard dimension inference

Point input now keeps an `AcceptedSnap` alongside each point a command
collects: the paper point, the model point it came from, the viewport and
frame it was seen through, and the geometry identity the snap engine
attributed. Interactive picks record in the click handler, typed / dynamic /
headless points record in `feed_command`, and the list is cleared whenever a
command starts or the active space changes. Commands that don't care keep
consuming the plain paper point unchanged; PR2 reads the model point and
frame, PR3 the source.

Dimension association inference is suppressed when the dimension's points came
through a viewport. Inference matches geometry against the dimension's own
definition points in whatever space it is handed, so paper definition points
projected from a viewport would associate with unrelated paper-sheet geometry
at those coordinates, or match model geometry using paper coordinates. An
empty source list makes `attach_dimension_association` a no-op. PR3 replaces
this with real viewport-aware associations.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/app/mod.rs

@@ -707,6 +707,25 @@ pub(super) struct OpenCADStudio {
     show_layout_tabs: bool,
     /// Last point committed by a drawing command — used as ortho/polar base.
     last_point: Option<glam::DVec3>,
+    /// Viewport frame the live snap marker is currently looking through (PR1).
+    /// Set by the cursor-move handler when the displayed snap came from a
+    /// layout viewport, cleared otherwise. Display/bookkeeping only — the point
+    /// itself is already projected onto the sheet.
+    pub(crate) vp_snap_frame: Option<crate::scene::viewport_ref::ViewportFrame>,
+    /// Snaps accepted by the active command's point steps, parallel to the
+    /// points it collected (PR1). A command that does not care keeps using the
+    /// plain paper point; dimension commands (PR2) read the model point,
+    /// viewport and frame from here, and PR3 reads `source`. Cleared whenever a
+    /// command starts or ends.
+    accepted_snaps: Vec<crate::scene::viewport_ref::AcceptedSnap>,
+    /// Snap resolved by the click currently being handled, with the viewport
+    /// frame it came through (PR1). Set inside the click handler's point
+    /// resolution so the point-accept path further down can record the
+    /// [`crate::scene::viewport_ref::AcceptedSnap`] without recomputing.
+    pending_click_snap: Option<(
+        crate::snap::SnapResult,
+        Option<crate::scene::viewport_ref::ViewportFrame>,
+    )>,
     /// Endpoint + unit exit-tangent of the most recently drawn line/arc, so
     /// `ARC_CONT` (Arc → Continue) can start tangentially from where drawing
     /// ended. `None` once a non-line/arc entity is committed.
@@ -3689,6 +3708,9 @@ impl OpenCADStudio {
             show_file_tabs: true,
             show_layout_tabs: true,
             last_point: None,
+            vp_snap_frame: None,
+            accepted_snaps: Vec::new(),
+            pending_click_snap: None,
             main_window: None,
             thumbnail_capture_clean: false,
             #[cfg(not(target_arch = "wasm32"))]